Respect service window of nextcloud

[FadeFx]

Description
Next loud 28.x asks to set up a service window, it would be cool if ncp could respect this for it's update and other tasks that put nextcloud in service mode temporary.

Example

If the nextcloud service window is set to start at 2am, then the update nextcloud and update nc-apps should be scheduled at that time.

[theCalcaholic]

That's a very good idea, albeit it's not very easy to implement with the current architecture of NextcloudPi. I'm planning a larger rewrite though and will keep this in mind