feat: command to run only the sidecar RPC and not the "core" indexer of the sidecar

[seanmcgary]

Currently, the Sidecar and its RPC server are a monolithic process. For simple use-cases where a highly available RPC is not required, this works fine.

However, if you would like to run a Sidecar with highly a highly available RPC, a single process will likely result in downtime during upgrades and becomes a single point of failure.

This ticket proposes introducing the ability to run the Sidecar RPC server as a separate process (or series of processes) that reads from the same database as the "primary" Sidecar process which would contain the indexer. Sidecar RPC-only processes could connect to the same database instance or even a read-only replica to reduce load on the database responsible for accepting writes. RPC endpoints that result in modifying or creating new state (e.g. rewards generation) would need to proxy their requests back to the "primary" Sidecar's RPC. RPCs that are read only could be handled directly in the RPC process.