Docs: Update documentation to reflect protected tags behavior
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- [x] Start this issue's title with `Docs:` or `Docs feedback:`.
## Problem to solve
This issue is to document the tag improvements in the following docs pages:
- [Protected tags](https://docs.gitlab.com/user/project/protected_tags/)
- [Protected tags API](https://docs.gitlab.com/api/protected_tags/)
## Other links/references
- Epic: https://gitlab.com/groups/gitlab-org/-/work_items/19673+
issue