[Merge] ~utkarsh/ubuntu/+source/systemd/+git/systemd:drop-time-daemon-provides into ~ubuntu-core-dev/ubuntu/+source/systemd:ubuntu-mantic

[Philip Roche]

@juliank The problem that prompted this was the cloud-minimal seed @ https://ubuntu-archive-team.ubuntu.com/seeds/ubuntu.mantic/cloud-minimal and the ubuntu-cloud-minimal meta package depends on systemd-timesyncd. When trying to change time-daemon to chrony for example this would cause removal of systemd-timesyncd but also removal of ubuntu-cloud-minimal because ubuntu-cloud-minimal's dependencies are now broken. See https://code.launchpad.net/~philroche/ubuntu-seeds/+git/ubuntu/+merge/449589 for initial discussions.

This would result in all the other ubuntu-cloud-minimal dependencies being marked as auto-removable. This is not our intention.

The goal here was to solve the above problem but also satisfy the following test cases/use cases:

* A case where ubuntu-cloud-minimal (with time-daemon seeded) is installed on the system. Therefore would have systemd-timesyncd too. And then when we install chrony, it should not result in the removal of ubuntu-cloud-minimal but just systemd-timesyncd (and time-daemon if that's what it takes). Right now, installation of chrony, removes ubuntu-cloud-minimal in our GCE image and we definitely don't want that.
* A case where we have chrony installed on the system but want to change to systemd-timesyncd. Is chrony removed? 
* A case where we have chrony and then we install ubuntu-cloud-minimal. The outcome should be removal of chrony in favor of systemd-timesyncd (via seeded time-daemon).
* A case for non minimal/base images that have neither ubuntu-cloud-minimal or time-deamon (non virtual package) installed. What happens if I install chrony? Is systemd-timesyncd still removed? If I then later install systemd-timesyncd, does it remove chrony?

> add a default-time-daemon provides to systemd-timesyncd or a default-time-daemon meta package

Would this solve the above cases?
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https://code.launchpad.net/~utkarsh/ubuntu/+source/systemd/+git/systemd/+merge/449863
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