Follow-up from "Add deploy_key associations and validations to protected tags"

The following discussion from !109911 (merged) should be addressed:

• @tle_gitlab started a discussion: (+1 comment)

  suggestion (non-blocking): I can see there are some standard codes shared between this and ProtectedBranch::PushAccessLevel. There might be an opportunity to move them into a helper class. Happy to have it explored in a separate issue. WDYT?