Enable frozen string for the following files:

* lib/gitlab/auth/**/*.rb
* lib/gitlab/badge/**/*.rb
* lib/gitlab/bare_repository_import/**/*.rb
* lib/gitlab/bitbucket_import/**/*.rb
* lib/gitlab/bitbucket_server_import/**/*.rb
* lib/gitlab/cache/**/*.rb
* lib/gitlab/checks/**/*.rb

Partially addresses #47424.