Docs update release checklist

What does this MR do?

Updates the Release Checklist template and generation script to include steps required for releasing Runner's Helm Chart.

Why was this MR needed?

Please read #3782 (closed) for details.

Are there points in the code the reviewer needs to double check?

BLOCKED BY charts/gitlab-runner!74 and charts/gitlab-runner!75

Does this MR meet the acceptance criteria?

• [-] Documentation created/updated
• [-] Added tests for this feature/bug
• In case of conflicts with master - branch was rebased

What are the relevant issue numbers?

Closes #3782 (closed)