Support yang model for buffer pool percentage (sonic-net#19358)

#### Why I did it

Support yang model for `percentage` field in `BUFFER_POOL` table.
It is used in dynamic buffer model only and represents the percentage of a buffer pool's size compared to the available memory size

#### How I did it

#### How to verify it

Unit test and manual test

Author: stephenxs

src/sonic-yang-models/doc/Configuration.md

@@ -573,6 +573,7 @@ When the system is running in traditional buffer model, the size of all of the b
 ```
 
 When the system is running in dynamic buffer model, the size of some of the buffer pools can be omitted and will be dynamically calculated.
+In this case, A percentage can be configured on a pool, representing how many the available buffer can be allloced to the pool.
 
 ```
 {
@@ -584,11 +585,12 @@ When the system is running in dynamic buffer model, the size of some of the buff
     },
     "egress_lossy_pool": {
         "type": "egress",
-        "mode": "dynamic",
+        "mode": "dynamic"
     },
     "ingress_lossless_pool": {
         "type": "ingress",
         "mode": "dynamic",
+        "percentage": "80"
     }
   }
 }

src/sonic-yang-models/tests/files/sample_config_db.json

@@ -36,6 +36,11 @@
                 "size": "12766208",
                 "type": "egress",
                 "mode": "dynamic"
+            },
+            "ingress_percentage_pool": {
+                "type": "ingress",
+                "mode": "dynamic",
+                "percentage": "90"
             }
         },
         "BUFFER_PROFILE": {
@@ -351,6 +356,7 @@
         },
         "DEVICE_METADATA": {
             "localhost": {
+                "buffer_model": "dynamic",
                 "type": "ToRRouter",
                 "asic_id": "06:00.0",
                 "mac": "00:11:22:33:dd:5a",

src/sonic-yang-models/tests/yang_model_tests/tests/buffer_pool.json

@@ -39,5 +39,23 @@
     "BUFFER_POOL_WRONG_SIZE_VALUE": {
         "desc": "BUFFER_POOL_WRONG_SIZE_VALUE pattern failure.",
         "eStr": "wrong"
+    },
+    "BUFFER_POOL_CORRECT_PERCENTAGE_VALUE": {
+        "desc": "BUFFER_POOL_CORRECT_PERCENTAGE_VALUE no failure."
+    },
+    "BUFFER_POOL_CORRECT_LARGE_PERCENTAGE_VALUE": {
+        "desc": "BUFFER_POOL_CORRECT_PERCENTAGE_VALUE no failure."
+    },
+    "BUFFER_POOL_WRONG_PERCENTAGE_NEGATIVE_VALUE": {
+        "desc": "BUFFER_POOL_WRONG_PERCENTAGE_NEGATIVE_VALUE pattern failure.",
+        "eStr": "Invalid value"
+    },
+    "BUFFER_POOL_WRONG_PERCENTAGE_NOT_A_NUMBER_VALUE": {
+        "desc": "BUFFER_POOL_WRONG_PERCENTAGE_NOT_A_NUMBER_VALUE pattern failure.",
+        "eStr": "Invalid value"
+    },
+    "BUFFER_POOL_WRONG_PERCENTAGE_VALUE_WITH_SIZE": {
+        "desc": "BUFFER_POOL_WRONG_PERCENTAGE_VALUE_WITH_SIZE pattern failure.",
+        "eStr": "Percentage should not be configured along with size"
     }
 }

src/sonic-yang-models/tests/yang_model_tests/tests_config/buffer_pool.json

@@ -167,5 +167,90 @@
                 ]
             }
         }
+    },
+    "BUFFER_POOL_CORRECT_PERCENTAGE_VALUE": {
+        "sonic-device_metadata:sonic-device_metadata": {
+            "sonic-device_metadata:DEVICE_METADATA": {
+                "localhost":{
+                        "buffer_model": "dynamic"
+                }
+            }
+        },
+        "sonic-buffer-pool:sonic-buffer-pool": {
+            "sonic-buffer-pool:BUFFER_POOL": {
+                "BUFFER_POOL_LIST": [
+                {
+                    "name": "ingress_lossless_pool",
+                    "mode": "dynamic",
+                    "percentage": "99",
+                    "type": "ingress"
+                }
+                ]
+            }
+        }
+    },
+    "BUFFER_POOL_CORRECT_LARGE_PERCENTAGE_VALUE": {
+        "sonic-device_metadata:sonic-device_metadata": {
+            "sonic-device_metadata:DEVICE_METADATA": {
+                "localhost":{
+                        "buffer_model": "dynamic"
+                }
+            }
+        },
+        "sonic-buffer-pool:sonic-buffer-pool": {
+            "sonic-buffer-pool:BUFFER_POOL": {
+                "BUFFER_POOL_LIST": [
+                {
+                    "name": "ingress_lossless_pool",
+                    "mode": "dynamic",
+                    "percentage": "200",
+                    "type": "ingress"
+                }
+                ]
+            }
+        }
+    },
+    "BUFFER_POOL_WRONG_PERCENTAGE_NEGATIVE_VALUE": {
+        "sonic-buffer-pool:sonic-buffer-pool": {
+            "sonic-buffer-pool:BUFFER_POOL": {
+                "BUFFER_POOL_LIST": [
+                {
+                    "name": "ingress_lossless_pool",
+                    "mode": "static",
+                    "percentage": "-10",
+                    "type": "ingress"
+                }
+                ]
+            }
+        }
+    },
+    "BUFFER_POOL_WRONG_PERCENTAGE_NOT_A_NUMBER_VALUE": {
+        "sonic-buffer-pool:sonic-buffer-pool": {
+            "sonic-buffer-pool:BUFFER_POOL": {
+                "BUFFER_POOL_LIST": [
+                {
+                    "name": "ingress_lossless_pool",
+                    "mode": "static",
+                    "percentage": "NaN",
+                    "type": "ingress"
+                }
+                ]
+            }
+        }
+    },
+    "BUFFER_POOL_WRONG_PERCENTAGE_VALUE_WITH_SIZE": {
+        "sonic-buffer-pool:sonic-buffer-pool": {
+            "sonic-buffer-pool:BUFFER_POOL": {
+                "BUFFER_POOL_LIST": [
+                {
+                    "name": "ingress_lossless_pool",
+                    "mode": "static",
+                    "percentage": "90",
+                    "size": "12766208",
+                    "type": "ingress"
+                }
+                ]
+            }
+        }
     }
 }

src/sonic-yang-models/yang-models/sonic-buffer-pool.yang

@@ -2,6 +2,10 @@ module sonic-buffer-pool {
     namespace "http://github.com/sonic-net/sonic-buffer-pool";
     prefix bpl;
 
+    import sonic-device_metadata {
+        prefix device_metadata;
+    }
+
     organization
         "SONiC";
 
@@ -57,6 +61,20 @@ module sonic-buffer-pool {
                     type uint64;
                     description "Buffer Pool Xoff Threshold (in Bytes)";
                 }
+
+                leaf percentage {
+                    type uint8;
+                    description "
+                        Buffer Pool percentage.
+                        The buffer pool size will be available_buffer * percentage / 100 if percentage is provided.
+                        It is valid in dynamic buffer model only.";
+                    must "(not(current()/../size))" {
+                        error-message "Percentage should not be configured along with size";
+                    }
+                    must "/device_metadata:sonic-device_metadata/device_metadata:DEVICE_METADATA/device_metadata:localhost/device_metadata:buffer_model = 'dynamic'" {
+                        error-message "Percentage must be configured in dynamic buffer model";
+                    }
+                }
             }
         }
     }