This PR makes the following changes:

Makes the RPC/WS endpoints match Geth

Rather than use custom paths for RPC/WS endpoints, Geth has the RPC and WS servers listen on different ports. This PR makes proxyd match that behavior. To configure Proxyd in this mode, use the following configuration:

[server]
# Host for the proxyd RPC server to listen on.
rpc_host = "0.0.0.0"
# Port for the above.
rpc_port = 8080
# Host for the proxyd WS server to listen on.
ws_host = "0.0.0.0"
# Port for the above
ws_port = 8085
# Maximum client body size, in bytes, that the server will accept.
max_body_size_bytes = 10485760

Better logging

This PR adds logging to all incoming requests, attempted WS connections, and exchanged WS messages. Additionally, it adds a randomly-generated req_id field to log output that will allow us to trace requests as they go from the web server, to the proxied backend, and back.

Example WS logs:

INFO [11-09|15:31:09.261] received WS connection                   req_id=63cfe34c38d6faec0989
INFO [11-09|15:31:09.774] accepted WS connection                   auth=foobar req_id=63cfe34c38d6faec0989
INFO [11-09|15:31:27.599] error preparing client message           auth=foobar req_id=63cfe34c38d6faec0989 err="parse error"
INFO [11-09|15:31:33.844] forwarded WS message to backend          method=eth_subscribe auth=foobar req_id=63cfe34c38d6faec0989
INFO [11-09|15:31:33.924] forwarded WS message to client           auth=foobar req_id=63cfe34c38d6faec0989

RPC:

INFO [11-09|15:34:07.287] received RPC request                     req_id=9293a41182a3bbb840fd auth=foobar
INFO [11-09|15:34:07.817] forwarded RPC request                    method=eth_blockNumber auth=foobar req_id=9293a41182a3bbb840fd

Change to how websocket backend groups are defined

Only one backend group can be websocket-enabled. Previously, this was done by defining a ws_enabled property on the backend group to proxy websockets to. To make this simpler, you can now define a single ws_backend_group config property at the top of the file. Example:

# List of WS methods to whitelist.
ws_method_whitelist = [
  "eth_subscribe",
  "eth_call",
  "eth_chainId"
]
# Enable WS on this backend group. There can only be one WS-enabled backend group.
ws_backend_group = "main"

[backends]
# A map of backends by name.
[backends.infura]
# The URL to contact the backend at.
rpc_url = "foo"
# The WS URL to contact the backend at.
ws_url = "bar"
max_rps = 3
max_ws_conns = 1

[backend_groups]
[backend_groups.main]
backends = ["infura"]

Note that all backends in the websocket backend group need a websocket URL.

The WS backend group is explicitly defined in the config rather than populated from the backends that have ws_urls because we may want the flexibility to create a custom group just for websocket-enabled endpoints in the future.