Update notifications via notifications API

[nickvergessen]

Core and app updates are checked every 24h via a background job.

Via the notifications API the update notification is then also available in the sync client and therefor helps people to remember to update their instances, even though they never check the web
UI.

The admin can pick a custom group of users to notify for updates. This is useful for “secure installations” where no syncing user is an admin.
Restriction:

• Core update notification is only available for update channels: beta, stable and production
• App updates are checked against the app store only

@carlaschroder

[phil-davis]

For clarification, I think you mean "checked every 24 hours"

[carlaschroder]

Nice, thanks @nickvergessen

[settermjd]

@phil-davis is this still required?