Put some Xen text into Bookworm release notes.

We should get some content into the official release notes document for Bookworm, since that's the way to overcome a chicken/egg problem. Putting stuff into NEWS or README is nice, but it can't be read before upgrading. ;]

Examples of content are:

• Do not use "aptitude full-upgrade" to do the upgrade to Xen 4.1X, since it tries to be overly helpful and already runs autoremove, which will remove e.g. xen-utils-4.11 when the 4.11 hypervisor is still running, resulting in a system where the user cannot shut down virtual machines any more before rebooting.
• Be aware that after when qemu is used to run HVM type virtual machines, it will not be possible to start a virtual machine again before rebooting the host machine because the new qemu links to the new Xen version libraries and the old hypervisor version is still running.
• In general, strongly recommend to not do anything else than shutting down or saving the running domUs and rebooting the host machine ASAP after upgrading the Xen packages.

So, task here:

1. Agree on what section in the release notes would be best to add this. (Near '4.6. Upgrading your kernel and related packages'? Or, an entry in '5.3. Package specific issues'?
2. Morph the stuff above into proper text.
3. File bug against release-notes with ready-made contents and request to add the text.

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Content from the pad:

Debian 12 Release Notes

Note: The goal is not to write as many things as possible in the release notes. It's really for the stuff that users otherwise might run into, because everything(tm) is not optimal and bug-free. So, 'less is more', in that sense.

• Tips and tricks for upgrading
• In which situations do you really want to first shut down domU
• qemu-system-xen -> this is about that new package, so that qemu (without xen) users can remove xen libs if they don't need them... but... hm... that should go into qemu release notes, and not xen? -> This is about xen now depeding on qemu-system-xen for HVM (and other dom0 qemu stuff) while it was qemu-system-x86 untill bullseye
• We could add some info about: Debian X is shipping with Xen Y, which has bugfix support until T1 and security support until T2
• open bug on "package release-notes in unstable": PV dropped for i386 domU
• open bug on "package release-notes in unstable": upgrading a xen VM to bookworm will change network interface name to predictable scheme. This is VERY important for remote upgrades: will break configured network connectivity
• The installer thing...
• update-grub added GRUB_DISABLE_OS_PROBER and it defaults to false. "running os-prober can cause damage to those guest OSes as it mounts filesystems" (ask Maney)
• Add ideas here... Ask yourself: did I ever run into something that I'd like to have known before, during upgrade...