1. Introduced better management of block snapshot files, now keeping list of files in the database, as well as options to recreate it from file system or via grpc communication (for RPC daemon).
2. Fixed small memory leak in header downloading.
3. Introduced (initial version) config command line flag to organise other flags into a .toml or .yaml files.
4. Better separated of RPC services into authenticted (for POS engine API) and non authenticated. Now only erigon itself runs authenticated service, but not any stand-alone RPC daemons.
5. Renamed engine.* flags to authrc.* command line flags for better consistency with go-ethereum.
6. Fixed panic in event subsriptions due to concurrent map access.