Add caching layer for fetching blocks information

[MakMuftic]

As multiple services fetch the same blocks from the same chains, the gateway should have a caching layer that allows us to call the RPC endpoint only once and return block information multiple times.

The caching layer should only hold a couple of minutes' worth of blocks saved.

This will reduce considerably our usage of RPC calls.

Implementation details

TBD

Testing details

• Manually validate that consecutive calls for the same block only use one RPC call
• Expand unit tests

Acceptance Criteria

• RPC Gateway only uses one RPC call to respond to consecutive RPC calls for the same block (or range)

QA Details