EVM node: support websocket connections for JSONRPC API

What

A websocket connection can be established on /ws (and /private/ws) to communicate with the EVM node JSONRPC API using websockets.

Fixes #7591 (closed).

Why

How

Depends on !15560 (merged).

Manually testing the MR

dune exec etherlink/tezt/tests/main.exe -- websocket /ci_disabled