Cache API responses

[csc-felipe]

Proposed solution

A caching solution would speed up returning responses, especially for larger ones, which can take dozens of seconds. It should be investigated if caching Swift backend responses, our own, or both.

DoD (Definition of Done)

There is a caching backend in place, such as Redis, which caches responses. There is a clear performance improvement from the UX.

Testing

Unit tests to make sure caching works, peer review for the speed-ups.