Updates to meetpad's Jitsi Meet configuration

Last week, we refreshed our configuration defaults for the Jitsi Meet services which provide the teleconferencing features of our meetpad.opendev.org service. The primary behavior change you're likely to notice is that meeting room URLs first take you to a pre-join page now. This is a workaround for some browsers, particularly Firefox, treating the audio stream as unsolicited and automatically blocking it. Previously, that was responsible for causing confusing "I can't hear anyone else" problems for many users. If you had trouble with sound on our meetpad service before, please do try it again at your convenience and let us know if it helped (or more importantly, if it didn't). -- Jeremy Stanley