[Merge] ~enr0n/ubuntu-release-upgrader:ubuntu/main into ubuntu-release-upgrader:ubuntu/main

[Julian Andres Klode]

Review: Approve

This seems ok but I'd keep the ability to use separate .cfg such that if we need to split it up again, we can use it again.
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https://code.launchpad.net/~enr0n/ubuntu-release-upgrader/+git/ubuntu-release-upgrader/+merge/480726
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