It's not necessary to perform a full join, sending a conference IQ is
enough.

This functionality is being brought back for apps
that use ljm for its prosody logic but not for
video conferencing, ie Jitsi-Meet Spot. The desired
use is for Spot-TVs to be identifiable by their
jid alone and for the resource to be the part
that identifies them.

Include XMPP user's credentials in the
CONNECTION_FAILED/PASSWORD_REQUIRED error event.

With JitsiAuthConnection the API consumer has to:
1. JitsiConference.createAuthenticationConnection,
2. JitsiAuthConnecition.authenticateAndUpgradeRole,
3. Wait on the Promise of 2,
4. Maybe cancel the JitsiAuthConnection of 1.

With authenticateAndUpgradeRole the API consumer has to:
1. JitsiConference.authenticateAndUpgradeRole,
2. Wait on the thenableWithCancel of 1.
3. Maybe cancel the thenableWithCancel of 1.