Added cache interface and cachelib + noop implementations

[samredai]

Summary

This breaks out just the cache interface from #1180 and leaves out any use of the dependency injection anywhere. I've also added a NoOpCache implementation of the CacheInterface which makes it nicer to use the dependency while also keeping it optional (A NoOpCache has the same methods so no need to do a null check for the cache everywhere).

I also added the caching docs page that describes how this works and how someone can implement their own custom cache dependency.

Test Plan

Wrote some tests to get full coverage.

• PR has an associated issue: #
• make check passes
• make test shows 100% unit test coverage

Deployment Plan

Deploying this has no effect because it's not used anywhere yet.

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[agorajek]

This is super clear. Love it. Let's get it in and start using.

[shangyian]

LGTM! Thanks for adding