Control resources used by the databases better

[xgreenx]

The current code has 4 separate databases. While it makes sense to have a big cache and a number of allowed descriptors for on-chain and off-chain databases, relayer and gas price databases don't need a cache at all, and they can use only a few file descriptors for their work.

Definition of done

Remove usage of the cache for relayer and gas price databases(capacity should be None).
The number of descriptor used by relayer and gas price databases should be small and don't affect descriptors allowance for on-chain and off-chain databases.