Add optional structured logs of RPC related events

[rem1-dev]

Adding RPC related event logs that will be used in Blockstream Explorer project. The logs are structured as json object. This optional logging may be used in an enterprise/internal scenario for billing purposes. By default it's turned off.

The logs are controlled with a new --rpc-logging command line option. Command line option possible values, and example structured logs they produce, are as following:

• --rpc-logging full results in logs:

ELECTRUM-RPC-LOGGER: {"event":"connection established","source":{"ip":"127.0.0.1","port":59877}}
ELECTRUM-RPC-LOGGER: {"event":"rpc request","id":18,"method":"blockchain.scripthash.get_history","params":["6b63eef944d982701eb2d0dbb8ee900f42d8e79fe3d1ea473602c0edc87c34f6"],"source":{"ip":"127.0.0.1","port":59877}}
ELECTRUM-RPC-LOGGER: {"duration_µs":114,"event":"rpc response","id":18,"method":"blockchain.scripthash.get_history","payload_size":37,"source":{"ip":"127.0.0.1","port":59877}}
ELECTRUM-RPC-LOGGER: {"event":"connection closed","source":{"ip":"127.0.0.1","port":59877}}

• --rpc-logging no-params excludes RPC request params to be logged, results in logs like:

ELECTRUM-RPC-LOGGER: {"event":"connection established","source":{"ip":"127.0.0.1","port":59886}}
ELECTRUM-RPC-LOGGER: {"event":"rpc request","id":18,"method":"blockchain.scripthash.get_history","params":null,"source":{"ip":"127.0.0.1","port":59886}}
ELECTRUM-RPC-LOGGER: {"duration_µs":78,"event":"rpc response","id":18,"method":"blockchain.scripthash.get_history","payload_size":37,"source":{"ip":"127.0.0.1","port":59886}}
ELECTRUM-RPC-LOGGER: {"event":"connection closed","source":{"ip":"127.0.0.1","port":59886}}```

[shesek]

Thanks @rem1-dev!