Use of `notify_push` with `nextcloudcmd` for headless server syncing

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Feature request

Which Nextcloud Version are you currently using: (see administration page)
32.0.5

Is your feature request related to a problem? Please describe.
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Currently there's not Official sync client for use on Headless servers which run as daemon or background service.

Describe the solution you'd like
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Would be great if nextcloudcmd could be altered to have support for Notify_push (so it knows when to download) and watch the filesystem (so it knows when to upload).

But in the mean time, one can sort of create this themselves by triggering nextcloudcmd based on inotifywait - but for the other side, how can one trigger nextcloudcmd from the test_client when it receives an event?

Describe alternatives you've considered
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forking the desktop client to be GUI less - but this is a really large undertaking.

Additional context
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I want to setup a client on a QNAP TS-133 - so it sync the online with an offline, this way local computers can use the local internet speed of the NAS, and remote computers can still see the updates

Start by reading the nextcloudcmd and test_client entry points mentioned in the request, then trace how notify_push events are received and how inotifywait currently triggers syncing. Define the intended headless-server workflow and its completion criteria before estimating an implementation.