[202405][wcmp]: Add W-ECMP to BGP OA

[nazariig]

HLD: https://github.com/sonic-net/SONiC/pull/1629

Why I did it

• W-ECMP feature implementation is according to the HLD

Work item tracking

• N/A

How I did it

• Added W-ECMP YANG model implementation
• Added W-ECMP BGP OA implementation

How to verify it

1. Run UTs
2. Verified manually with the feature qualification

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

• [ ] 201811
• [ ] 201911
• [ ] 202006
• [ ] 202012
• [ ] 202106
• [ ] 202111
• [ ] 202205
• [ ] 202211
• [ ] 202305
• [X] 202405

Tested branch (Please provide the tested image version)

• [X] 202405

Details if related

• Backport from master: https://github.com/sonic-net/sonic-buildimage/pull/18533

Description for the changelog

• N/A

Link to config_db schema for YANG module changes

• N/A

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

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