Introduce a yjs websocket client for XWiki

To integrate Blocknote with XWiki, a websocket endpoints handling yjs will be introduced on XWiki (see XWIKI-23158).
This endpoint is expected special messages. Therefore, a custom client will also need to be provided by cristal for the xwiki backend.
This work will also require some change in the way we inject the connector in Blocknote (i.e., currently hardcoded)