Rename to protected packages
What does this MR do and why?
Change Package protection rules API
to Protected packages API
for parity with https://docs.gitlab.com/ee/user/packages/package_registry/package_protection_rules.html.
This follows an extended discussion from some time ago where it was decided to run with "protected packages" as the feature name. I'll leave the topic titles in place because the API still technically operates on the rules.