[GCU] Moving PatchSorter unit-test to json file to make it easier to read/maintain (sonic-net#1977)

#### What I did
Moved PatchSorter unit-test to json file to make it easier to read/maintain

In the future this test json file can be used for adding nightly tests.

While testing I had to set `skip_exact_change_list_match=True` because different runs of the same input produce correct but different changes. It is better to always generate the same steps for easier debugging. Created issue: sonic-net#1976

#### How I did it
Copied to Json file the following:
- current_config i.e. current running config
- patch 
- expected change list

#### How to verify it
unit-tests

Author: ghooo

tests/generic_config_updater/files/patch_sorter_test_failure.json

@@ -0,0 +1,71 @@
+{
+    "EMPTYING_A_CONFIGDB_TABLE__FAILURE": {
+        "desc": "Emptying a configdb table fails because empty tables are not allowed in configdb. User should remove whole table instead e.g. remove /ACL_TABLE in this case.",
+        "current_config": {
+            "ACL_TABLE": {
+                "EVERFLOW": {
+                    "policy_desc": "EVERFLOW",
+                    "ports": [
+                        "Ethernet0"
+                    ],
+                    "stage": "ingress",
+                    "type": "MIRROR"
+                }
+            },
+            "PORT": {
+                "Ethernet0": {
+                    "alias": "Eth1",
+                    "lanes": "65, 66, 67, 68",
+                    "description": "Ethernet0 100G link",
+                    "speed": "100000"
+                }
+            }
+        },
+        "patch": [
+            {"op": "remove", "path": "/ACL_TABLE/EVERFLOW"}
+        ],
+        "expected_error_substrings": [
+            "There is no possible sorting"
+        ]
+    },
+    "ADDING_AN_EMPTY_CONFIGDB_TABLE__FAILURE": {
+        "desc": "Adding an empty configdb table fail because empty tables are not allowed in configdb.",
+        "current_config": {},
+        "patch": [
+            {"op": "add", "path": "/VLAN", "value": {}}
+        ],
+        "expected_error_substrings": [
+            "There is no possible sorting"
+        ]
+    },
+    "EMPTYING_MULTIPLE_CONFIGDB_TABLE__FAILURE": {
+        "desc": "Emptying multiple configdb table fails because empty tables are not allowed in configdb. User should remove whole tables instead  e.g. remove /PORT and /ACL_TABLE in this case.",
+        "current_config": {
+            "ACL_TABLE": {
+                "EVERFLOW": {
+                    "policy_desc": "EVERFLOW",
+                    "ports": [
+                        "Ethernet0"
+                    ],
+                    "stage": "ingress",
+                    "type": "MIRROR"
+                }
+            },
+            "PORT": {
+                "Ethernet0": {
+                    "alias": "Eth1",
+                    "lanes": "65, 66, 67, 68",
+                    "description": "Ethernet0 100G link",
+                    "speed": "100000"
+                }
+            }
+        },
+        "patch": [
+            {"op": "remove", "path": "/ACL_TABLE/EVERFLOW"},
+            {"op": "remove", "path": "/PORT/Ethernet0"}
+        ],
+        "expected_error_substrings": [
+            "There is no possible sorting"
+        ]
+    }
+}