Basic implementation of Caching Middleware

[evgeniy-scherbina]

Documentation: https://github.com/Kava-Labs/kava-proxy-service/blob/yevhenii/cache/architecture/CACHING.md

[galxy25]

in addition to the requested changes in the comments

• Update developer docs with notes on what type of cache is used
• Add new architecture docs for how the cache works, and how it modifies the proxy request flow, and how to debug it when something goes wrong
• finish out todo’s
• add docs on how to invalidate the cache (either all keys or for specific methods)
• add e2e integration test in main_test.go that verifies when a cacheable request is sent to the proxy service it does get cached in the local docker redis

[galxy25]

@evgeniy-scherbina we'll want to be able to flip the cache on or off via an environment variable (e.g. some if block in those middleware that is checked first before running any of the caching specific code and hands off to the next handler if the cache is configured to be disabled) in cases where there is a bug that is safer / faster to bypass in production by disabling the cache, and to allow debugging to correctly triage if any observed issues with the proxy are related to the caching code paths

[evgeniy-scherbina]

@evgeniy-scherbina any idea why the github actions e2e and unit tests aren't running for this PR?

there were conflicts