Mark spec.selector as required in ReplicationController and add tests

[priyansh3006]

What type of PR is this?
/kind feature

What this PR does / why we need it:

1.This change adds the +k8s:required tag to the spec.selector field in ReplicationController and includes validation tests to ensure an empty selector fails and a valid selector passes.
2. This change adds the +k8s:required tag to the template field in ReplicationControllerSpec to enforce its mandatory status in the API schema and includes corresponding validation tests for both nil (failure) and valid (success) scenarios.

Which issue(s) this PR is related to:
part of #134280

Special notes for your reviewer:
Code generation , Declarative Validation and fuzz testing are already enabled for ReplicationController as it is part of the core API group (group="", version="v1"), which is already registered

Does this PR introduce a user-facing change?
No

Additional documentation, e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:
[KEP]:

https://github.com/kubernetes/enhancements/blob/master/keps/sig-api-machinery/5073-declarative-validation-with-validation-gen/README.md

[k8s-ci-robot]

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[k8s-ci-robot]

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[k8s-ci-robot]

Hi @priyansh3006. Thanks for your PR.

I'm waiting for a github.com member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: priyansh3006
Once this PR has been reviewed and has the lgtm label, please assign smarterclayton for approval. For more information see the Code Review Process.

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Needs approval from an approver in each of these files:

• pkg/apis/OWNERS
• pkg/registry/core/replicationcontroller/OWNERS
• staging/src/k8s.io/api/OWNERS

Approvers can indicate their approval by writing /approve in a comment
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[k8s-triage-robot]

This PR may require API review.

If so, when the changes are ready, complete the pre-review checklist and request an API review.

Status of requested reviews is tracked in the API Review project.

[priyansh3006]

I am considering migrating ReplicationControllerStatus's Components with +k8s:minimum=0 since they are manually checked for non-negative values. Should I include this in the current PR or open a separate one?

[aaron-prindle]

/ok-to-test

/cc @aaron-prindle @yongrulin @lalitc375