Allow protected branch creation for empty project

What does this MR do?

Fixes the bug wherein on a new repo, no one can push to master.

Adds a check on Gitlab::Checks::BranchCheck#protected_branch_checks that will check if the project is empty, it won't run protected_branch_creation_checks but instead will defer to protected_branch_push_checks.

What are the relevant issue numbers?

#58613 (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 #58613 (closed)