Refactor Branch related services to move to `branches` folder

What does this MR do?

This is part of the effort to make the app/services folder sane.

This MR aggregates branch-related service classes into app/services/branches, so we can have related services closer to each other.

Part of the effort in #26319 (closed)

Conformity

• Code review guidelines
• Style guides
• Separation of EE specific content