[yang]DHCPv6 relay yang model is not up to date

[dgsudharsan]

Description

DHCPv6 yang model is not up to date. Certain new fields parsed in the code are not defined in the yang model. For e.g. dhcpv6_option|rfc6939_support and dhcpv6_option|interface_id are not defined in https://github.com/sonic-net/sonic-buildimage/blob/master/src/sonic-yang-models/yang-models/sonic-dhcpv6-relay.yang but parsed in https://github.com/sonic-net/sonic-dhcp-relay/blob/master/src/configInterface.cpp

Steps to reproduce the issue:

Describe the results you received:

DHCPv6 yang model is not updated

Describe the results you expected:

DHCPv6 yang model needs to be updated with all the fields

Output of show version:

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Output of show techsupport:

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Additional information you deem important (e.g. issue happens only occasionally):

[dgsudharsan]

@jcaiMR @zhangyanzhao @yxieca FYI

[dgsudharsan]

@jcaiMR @yxieca @kellyyeh Can you please provide ETA to fix the issue?

[kellyyeh]

@dgsudharsan ETA 2/28

[dgsudharsan]

@kellyyeh Please share the PR once its available

[dgsudharsan]

@kellyyeh @jcaiMR @yxieca Can you please let us know when the PR will be available?

[kellyyeh]

Hi @dgsudharsan, please help review this PR #14144