follow-up(PublicShareAuthSidebar): sidebar doesn't track conversation removal

[Antreesy]

When requesting the password of a share it might be good to leave the room if the media settings screen is closed without joining the call. Leaving the call or the conversation should update the sidebar and remove the call view and the chat and show This conversation has ended, although it seems that was lost at some point 🤔 As leaving the call does not currently do that I guess it would be fine to leave the conversation when the media settings is closed in a follow up once the existing code was also fixed.

Originally posted by @danxuliu in #10633 (review)

With internal signling only, we fetch conversation within an interval, and show the context mentioned above.
With HPB setup sidebar waits for signaling message to fetch.

As a solution - we may track signaling message, that owner left the room, and fetch the conversation within some timeout => and if it was deleted, it should show This conversation has ended