[dhcp_relay] Update CLI reference document and add a new API for ip address type (sonic-net#1717)

#### What I did
Update CLI reference document following PR : sonic-net#8211
Add a new API on utilities_common to get IP type.

#### How I did it
- Update doc/Command-Reference.md with new DHCP CLI.
- Add ipaddress_type API to utilities_common/cli.py

#### How to verify it
- Build an image with PR sonic-net#8211 and this PR.
- Run DHCP CLI commands

Author: shlomibitton

doc/Command-Reference.md

@@ -2231,27 +2231,32 @@ This sub-section of commands is used to add or remove the DHCP Relay Destination
 
 **config vlan dhcp_relay add**
 
-This command is used to add a DHCP Relay Destination IP address to the a VLAN.  Note that more that one DHCP Relay Destination IP address can be added on a VLAN interface.
+This command is used to add a DHCP Relay Destination IP address or multiple IP addresses to a VLAN.  Note that more than one DHCP Relay Destination IP address can be added on a VLAN interface.
 
 - Usage:
   ```
-  config vlan dhcp_relay add <vlan_id> <dhcp_relay_destination_ip>
+  config vlan dhcp_relay add <vlan_id> <dhcp_relay_destination_ips>
   ```
 
 - Example:
   ```
   admin@sonic:~$ sudo config vlan dhcp_relay add 1000 7.7.7.7
-  Added DHCP relay destination address 7.7.7.7 to Vlan1000
+  Added DHCP relay destination address ['7.7.7.7'] to Vlan1000
+  Restarting DHCP relay service...
+  ```
+  ```
+  admin@sonic:~$ sudo config vlan dhcp_relay add 1000 7.7.7.7 1.1.1.1
+  Added DHCP relay destination address ['7.7.7.7', '1.1.1.1'] to Vlan1000
   Restarting DHCP relay service...
   ```
 
 **config vlan dhcp_relay delete**
 
-This command is used to delete a configured DHCP Relay Destination IP address from a VLAN interface.
+This command is used to delete a configured DHCP Relay Destination IP address or multiple IP addresses from a VLAN interface.
 
 - Usage:
   ```
-  config vlan dhcp_relay del <vlan-id> <dhcp_relay_destination_ip>
+  config vlan dhcp_relay del <vlan-id> <dhcp_relay_destination_ips>
   ```
 
 - Example:
@@ -2260,6 +2265,11 @@ This command is used to delete a configured DHCP Relay Destination IP address fr
   Removed DHCP relay destination address 7.7.7.7 from Vlan1000
   Restarting DHCP relay service...
   ```
+  ```
+  admin@sonic:~$ sudo config vlan dhcp_relay del 1000 7.7.7.7 1.1.1.1
+  Removed DHCP relay destination address ('7.7.7.7', '1.1.1.1') from Vlan1000
+  Restarting DHCP relay service...
+  ```
 
 Go Back To [Beginning of the document](#) or [Beginning of this section](#dhcp-relay)
 

utilities_common/cli.py

@@ -7,6 +7,7 @@
 
 import click
 import json
+import netaddr
 
 from natsort import natsorted
 from sonic_py_common import multi_asic
@@ -203,6 +204,17 @@ def is_ipaddress(val):
         return False
     return True
 
+def ipaddress_type(val):
+    """ Return the IP address type """
+    if not val:
+        return None
+
+    try:
+        ip_version = netaddr.IPAddress(str(val))
+    except netaddr.core.AddrFormatError:
+        return None
+
+    return ip_version.version
 
 def is_ip_prefix_in_key(key):
     '''