GCU add_cluster tests cases missing in 202511

[Anand Mehra]

Hi Rita, Abhishek,

Following PRs are missing in sonic-mgmt 202511 branch which adds the new test cases under generic_config_updater/add_cluster.

https://github.com/sonic-net/sonic-mgmt/pull/20913

https://github.com/sonic-net/sonic-mgmt/pull/14887

https://github.com/sonic-net/sonic-mgmt/pull/21882

https://github.com/sonic-net/sonic-mgmt/pull/22144

https://github.com/sonic-net/sonic-mgmt/pull/22859

Please help to get cherry-picked in 202511.

Thanks,

Anand Mehra