Merge the gitlab-shell "gitlab-keys" functionality into GitLab CE

What does this MR do?

Move the relevant code from gitlab-shell's GitlabKeys class to gitlab-rails as Gitlab::AuthorizedKeys.

Not all "commands" were kept as they are not being used in gitlab-rails. Also removed some methods in Gitlab::Shell that are using those "commands" as they're not being used.

What are the relevant issue numbers?

#56089 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [-] Documentation created/updated via this MR
• [-] Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• [-] Conforms to the database guides
• [-] Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer

Closes #56089 (closed)