Add support for namespaces RestoreItemAction plugin

[mouellet]

Please add a summary of your change

Namespaces are still lazily restored but using the normal restore process instead of directly from backup.

Does your change fix a particular issue?

Fixes #4478

Please indicate you've done the following:

• [x] Accepted the DCO. Commits without the DCO will delay acceptance.
• [ ] Created a changelog file or added /kind changelog-not-required as a comment on this pull request.
• [ ] Updated the corresponding documentation in site/content/docs/main.