♻️(frontend) get media 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 media url,
we refacto to remove the frontend env occurences
and to adapt with the new way to get the media url.

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

@@ -1,4 +1,3 @@
 NEXT_PUBLIC_API_ORIGIN=http://localhost:8071
 NEXT_PUBLIC_Y_PROVIDER_URL=ws://localhost:4444
-NEXT_PUBLIC_MEDIA_URL=http://localhost:8083
 NEXT_PUBLIC_SW_DEACTIVATED=true