A given recording should only trigger a single consent request.
The mechanism to notify about recording status updates may fire multiple
times since it's tied to XMPP presence and may send updates such as when
the live stream view URL is set.
Rather than trying to handle all possible corner cases to make sure we
only show the consent dialog once, keep track of the recording session
IDs for which we _have_ asked for consent and skip the dialog in case we
have done it already.
