Add caching to branches API [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

Adds caching of rendered JSON entities to the branches API. This results in about a 150ms response time improvement on my GDK, should be roughly similar in production.

Related #330128 (closed)

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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Security

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