Create Debian package

Analogous to https://salsa.debian.org/xmpp-team/sms4you/-/commit/6dcf2ccc13d4d2f962fafb96ba9a9ac54ce9fa18.

We also need packages for briar-gtk (briar-gtk!39 (merged)) and briar-headless (briar!1252 (closed)).

Closes #14 (closed)