save blocks to postgres and serve via RPC get_block()

[grooviegermanikus]

Store and expose blocks via RPC get_block method. It uses PostgreSQL database with a rolling per-epoch schema partitioning.
The feature is optional and can be turned on by:

• enable_postgres_block_store_importer: will run imp

Performance

Save time samples from lite-rpc service running on same machine as database. Note that this gives unrealistically low numbers!

Saving block 274506709@confirmed to postgres took 1.20ms for block and 89.53ms for 1701 transactions (4x500 chunks)
Saving block 274506710@confirmed to postgres took 1.23ms for block and 91.08ms for 1036 transactions (3x500 chunks)
Saving block 274506711@confirmed to postgres took 1.04ms for block and 68.03ms for 1042 transactions (3x500 chunks)
Saving block 274506713@confirmed to postgres took 1.45ms for block and 112.30ms for 2102 transactions (4x526 chunks)
Saving block 274506714@confirmed to postgres took 0.89ms for block and 85.43ms for 530 transactions (2x500 chunks)
Saving block 274506715@confirmed to postgres took 0.69ms for block and 59.01ms for 1274 transactions (3x500 chunks)
Saving block 274506716@confirmed to postgres took 1.23ms for block and 89.16ms for 1184 transactions (3x500 chunks)
Saving block 274506717@confirmed to postgres took 0.89ms for block and 114.35ms for 753 transactions (2x500 chunks)
Saving block 274506718@confirmed to postgres took 0.98ms for block and 121.74ms for 879 transactions (2x500 chunks)
Saving block 274506719@confirmed to postgres took 0.77ms for block and 91.44ms for 719 transactions (2x500 chunks)
Saving block 274506720@confirmed to postgres took 0.98ms for block and 119.94ms for 3158 transactions (4x790 chunks)
Saving block 274506721@confirmed to postgres took 1.03ms for block and 93.44ms for 1078 transactions (3x500 chunks)
Saving block 274506722@confirmed to postgres took 0.93ms for block and 80.33ms for 1015 transactions (3x500 chunks)
Saving block 274506723@confirmed to postgres took 1.00ms for block and 76.07ms for 1210 transactions (3x500 chunks)
Saving block 274506724@confirmed to postgres took 1.54ms for block and 169.81ms for 2487 transactions (4x622 chunks)
Saving block 274506725@confirmed to postgres took 1.02ms for block and 101.69ms for 1670 transactions (4x500 chunks)
Saving block 274506726@confirmed to postgres took 1.05ms for block and 90.57ms for 1661 transactions (4x500 chunks)

What's missing?

• The data model is not completed and only partially compatible with Full RPC.
• WS subscription is not there
• use PgBouncer for read connections