[YANG] Add valid v6 address to sonic-dhcp-sever.yang

[wen587]

Why I did it

The PR is to allow v6 address in DHCP_SERVER table which was generated from PROD minigraph. This is to pass the YANG validation.

Work item tracking

• Microsoft ADO (number only): 27552851

How I did it

Replace ipv4-address with ip-address which is a union of ipv4-address nad ipv6-address

How to verify it

Unit test

Which release branch to backport (provide reason below if selected)

• [ ] 201811
• [ ] 201911
• [ ] 202006
• [ ] 202012
• [ ] 202106
• [ ] 202111
• [ ] 202205
• [ ] 202211
• [ ] 202305

Tested branch (Please provide the tested image version)

• [ ]
• [ ]

Description for the changelog

Link to config_db schema for YANG module changes

A picture of a cute animal (not mandatory but encouraged)