Added service to find target branch rule branch

What does this MR do and why?

Creates the service that searches and returns the target branch rule target for the specified branch name. If the rule doesn't exist or then the default branch name will get returned.

Screenshots or screen recordings

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Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

#17909 (closed)