d/p/*: Select dhcp-client according to release

For releases with codename trixie and before select isc-dhcp-client, otherwise select dhcpcd-base. This way the dhcp-client installed in the container matches the one that comes with the respective release by default.

This patch also contains a workaround to deal with a hack applied in https://salsa.debian.org/salsa-ci-team/autopkgtest-lxc, commit 479b0daa166b90c26f8afa85eb5f174fc10cf0b2.