feat(api): Support combined HTTP / WS server

[slowli]

What ❔

• Supports combined HTTP / WS server bound to a single port.
• Allows configuring RPC namespaces for WS.

Why ❔

Improves UX for node operators.

Is this a breaking change?

• [ ] Yes
• [x] No

Operational changes

• HTTP / WS server is combined automatically if api.web3_json_rpc.{http_port, ws_port} are equal.
• RPC namespaces for WS are represented via new api.web3_json_rpc.ws_api_namespaces param. api.web3_json_rpc.api_namespaces is still used if the new param is not set.

Checklist

• [x] PR title corresponds to the body of PR (we generate changelog entries from PRs).
• [x] Tests for the changes have been added / updated.
• [x] Documentation comments have been added / updated.
• [x] Code has been formatted via zkstack dev fmt and zkstack dev lint.