System Update Daemon for Other Desktop Environments

### Problem

In other desktop environments, the daemon that handles system updates does not run at login. I understand this is by design as the daemon does a bunch of other stuff that could cause issues elsewhere. This practically means though that if you choose to use another desktop environment, unless you enable that daemon manually, you do not receive any system updates.

Please see discussion here for more: https://github.com/orgs/elementary/discussions/871

### Proposal

Either:

1) Add an option to, at the user's own risk, run io.elementary.settings-daemon at login even when they're not using Pantheon.

Or...

2) If that could cause issues, split system updates off into its own daemon and have it run automatically everywhere.

Thank you!
-Eri

### Prior Art (Optional)

_No response_