Update Gitlab::Git::TagPolicy to check if the current user can create tags

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The tag policy currently checks if the user can

      rule { can?(:admin_tag) & (~protected_tag | can?(:maintainer_access)) }.enable :delete_tag

Firstly this is written slightly strangely. The logical grouping should be (can?(:admin_tag) & ~protected_tag) | can?(:maintainer_access)

We also need to remove the maintainer_access condition and switch it out for a check that ensures the user is allowed to create the tag via the protected tag settings