Add automated maintenance

[Root-Core]

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• I have read the contributing guideline and understand that I have made the correct modifications

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Description:

This is a subset of #523 which only handles the maintenance parts.

Benefits of this PR and context:

There are some tasks that need to run after upgrades:

• occ db:add-missing-indices
• occ maintenance:repair --include-expensive

They usually don't take much time, but improve the performance of NextCloud.
They also remove warnings in the admin panel.

There is also a "new" config variable "maintenance_window_start", which defines when non time critical tasks are run. This improves the performance and user experience: https://docs.nextcloud.com/server/28/admin_manual/configuration_server/background_jobs_configuration.html#maintenance-window-start

How Has This Been Tested?

I tested it on major upgrades and multiple restarts.

Source / References:

#523

https://docs.nextcloud.com/server/28/admin_manual/configuration_server/background_jobs_configuration.html#maintenance-window-start

[LinuxServer-CI]

This pull request has been automatically marked as stale because it has not had recent activity. This might be due to missing feedback from OP. It will be closed if no further activity occurs. Thank you for your contributions.

[Root-Core]

Not stale, waiting for review.
CC @aptalca

[LinuxServer-CI]

This pull request has been automatically marked as stale because it has not had recent activity. This might be due to missing feedback from OP. It will be closed if no further activity occurs. Thank you for your contributions.

[Root-Core]

Still waiting for review.

[LinuxServer-CI]

This pull request has been automatically marked as stale because it has not had recent activity. This might be due to missing feedback from OP. It will be closed if no further activity occurs. Thank you for your contributions.

[Root-Core]

Still waiting for review.