feat(jitsi-meet): Add OpenDesk topbar in Jitsi UI

This PR adds OpenDesk topbar (with OpenDesk logo and navigation button) in Jitsi UI.

Since Jitsi doesn't have a web backend, it fetches the navigation data from the portal in the client side. So, related CORS headers are needed to send requests from the Jitsi domain (e.g. meet.nightly.opendesk.qa) to the portal domain (e.g. portal.nightly.opendesk.qa).

For the possible expired portal session, Jitsi refreshes the portal session by using a hidden iframe first and then it sends the request to the navigation endpoint (e.g. portal.nightly.opendesk.qa/univention/portal/navigation.json). Therefore it also needs Content-Security-Policy headers.

Edit: PR was updated to get the navigation data after a silent login. So, no need CORS or Content-Security-Policy headers anymore.