Add Debian 13 (Trixie) as a CI builder

We should prepare for Debian 13 and ensure an easy transition.

This task covers the addition of the following:

• Debian 13 builder on amd64, aarch64, ppc64le

The builder will run the following tests:

• autobake package building
• Comprehensive mtr runs, as for previous release package distros
• Install & Upgrade tests

As this will have to be done before we migrate to the new buildbot system, we will have this MDBF as part of the "Migration to new buildbot" epic.