Add confirm delete protected branch modal

What does this MR do?

• Allow masters, owners & admins to delete protected branches

Why was this MR needed?

• If an owner or master wanted to delete protected branch, they first had to go into settings and unprotect it before being able to remove it. Very inconvenient

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #21393 (closed)