Change label category:pods to category:cell

As a result of gitlab-com/www-gitlab-com!121163 (merged), we need to adjust the category labels from category:pods to category:cell. This can be applied both to open and closed issues, merge requests and epics.

Summary

This template is for new or renaming Category labels. This review helps to ensure there will be no impact with triage automation and reports.

Action items

• Link the merge request to www-gitlab-com for the category.yml change: Rename Category:Pods to Category:Cell (gitlab-com/www-gitlab-com!121163 - merged)
• (If applicable) Label migration on existing issues and merge requests: apply the new label to opened & closed issues, and open & merged merge requests.
• (If applicable) Rename the old label by adding [DEPRECATED] at the end of the label name, like ~"CI/CD [DEPRECATED]".

/cc @gitlab-org/quality/engineering-productivity @gl-quality/eng-prod