[Merge] ~juliank/livecd-rootfs:deb822-sources into livecd-rootfs:ubuntu/master

[Chad Smith]

Added a corresponding cloud-init branch[1] to update this template there. Your review is appreciated there once the text/suites/components and desired /etc/apt/sources.list.d/<somefile>.sources are settled.

[1] https://github.com/canonical/cloud-init/pull/4770
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https://code.launchpad.net/~juliank/livecd-rootfs/+git/livecd-rootfs/+merge/458366
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