docs: add EOL process documentation

[Rajkaran-122]

Adds comprehensive EOL process documentation that outlines how etcd versions reach end of life. The document includes version support policy, EOL process steps, announcement templates, criteria for EOL, and related documentation links. Also updates release.md to link to the new EOL documentation.

#22282

Also adds AGENTS.md for AI-assisted contributions to improve contribution quality and reduce duplicate submissions.

[kubernetes-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Rajkaran-122
Once this PR has been reviewed and has the lgtm label, please assign serathius for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[kubernetes-prow]

Hi @Rajkaran-122. Thanks for your PR.

I'm waiting for a etcd-io 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.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.