Update debian files and repos for bookworm release
Our files in debian/ should be for the current debian release; Debian bookworm release was 2023-06-10. This will also require us to update all the debian-alt files, the debian-alt/doc release documentation, the deb.i2p2.de website page, and the reprepro files. So plenty of chances to break things.
Typically we're not the fastest at doing this, not an emergency. But also probably should wait until #394 is fixed because that's a mess.