Branches page review

What does this MR do and why?

Reviews the Branches page. Make sure they align with the CTRT topics types and the Documentation Style Guide.

Proposed changes

• The protected_branches.md file is located in the doc/user/project/ directory. Change the location to doc/user/project/repository/branches/protected_branches.md.
• Organize headings in a more logical order:

  Before	After

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Related issues

• Issue: #480482 (closed)
• Task: #480488 (closed)