feat(gateway): cache indexer response

[kckeiks]

Why

Fixes #387

What

• Add cache in resolver and cache responses from indexer.
• Allow users to configure the cache.

Checklist

• I have made corresponding changes to the tests
• I have made corresponding changes to the documentation
• I have run the app using my feature and ensured that no functionality is broken

[kckeiks]

Numbers improved as expected. On average before adding the cache, the gateway was somewhere around ~3400 req/s and after adding the cache it was ~3900 req/s. The indexer was running locally. In production, there could potentially be more latency between indexer and gateway so the difference seen here could possibly be higher in prod.