♻️(frontend) get collaboration server url from config endpoint

We centralized the configuration on the backend
side, it is easier to manage and we can change
the configuration without having to rebuild the
frontend.
We now use the config endpoint to get the collaboration
server url, we refacto to remove the frontend env
occurences and to adapt with the new way to get the
collaboration server url.

src/frontend/apps/impress/.env.development

@@ -1,3 +1,2 @@
 NEXT_PUBLIC_API_ORIGIN=http://localhost:8071
-NEXT_PUBLIC_Y_PROVIDER_URL=ws://localhost:4444
 NEXT_PUBLIC_SW_DEACTIVATED=true