Dynamic secret generation

[conorsch]

Multiple secrets are required for authenticating the various components of the Jitsi Meet stack. The Debian package installation automatically generates most keys, but we'll need to read them from on disk in order to ensure idempotence while avoiding storing secrets on the Ansible host. The secrets are currently defined as:

• [x] jitsi_meet_videobridge_secret
• [x] jitsi_meet_jicofo_secret
• [x] jitsi_meet_jicofo_password

[conorsch]

Also need to create the pardir for /var/lib/prosody/* jicofo auth info.