feat(config): add server config + can disable message-bus

- server now provide it's config via /api/config (possibility to feature flag)
- client use /api/config to enable / disable some features
- capability to disable the message bus, somme OPS may not want this feature and
  consume persistent connections from server (websocket):
  OXICLOUD_MESSAGEBUS_ENABLE (true by default)

src/bin/generate-asyncapi.rs

@@ -186,7 +186,7 @@ fn operations() -> Value {
             ]
         },
         // Application-layer keepalive. Separate from the RFC 6455 Ping
-        // control frame the server sends on `OXICLOUD_RT_WS_KEEPALIVE_SECONDS`
+        // control frame the server sends on `OXICLOUD_MESSAGEBUS_KEEPALIVE_SECONDS`
         // (which is transport-level and not modelled in AsyncAPI). This
         // operation lets a client actively confirm the socket is
         // end-to-end alive when transport-level Pings alone can't rule