Add SUPPORT_END to os-release

On Tue, Nov 01, 2022 at 03:48:54PM -0000, Jeremy Bicha wrote:
> Public bug reported:

> There is a new suggested field to the os-release file: SUPPORT_END=YYYY-
> MM-DD

> If it is set, systemd 252 apparently sets a "support-ended" taint flag
> once that date has been reached.

"support" is a property of the product committments made around the OS, that
cannot definitively be known at the time of the GA release. Encoding it in
a file in the OS therefore carries an implicit obligation to update that
file whenever changes are made to the support committments. This does not
sound like something we want (in addition to already having to update
distro-info-data).

Why is it valuable for systemd to set this taint flag? We already have
Ubuntu-native mechanisms for notifying users they are out of support.

The approximate end of support date is known for the non-LTS releases. I think it's possible for Ubuntu Pro enablement to update /etc/os-release

Some parts of /etc/os-release are very useful (almost essential); other fields are less practical. Perhaps it's not worth the work to support this new field.