[Debian-rtc-admin] Upgrade prosody and prosody-modules to buster-backports versions on vogler

[Martin]

Dear Admins,

please upgrade prosody and prosody-modules on vogler to the
buster-backports versions instead of the stable versions.

There are many bug fixes and improvements from prosody 0.11.2 to
0.11.7 and in the > 1.5 years of development in the
prosody-modules.

Thank you very much in advance!

Cheers, Martin