Werk #16825: parent scan: Deprecate command line tool in favor of REST API endpoint

In this werk, we replace the cmk --scan-parents command line tool with a more flexible parent scan REST API endpoint.

As opposed to the command line option, the new endpoint will no longer create automatically-applied parents.mk config files but rely on the standard WATO configuration mechanism, so changes need to be activated afterwards.

Attention: Incompatibility, possible data loss in distributed monitoring setups

If you have previously used the parent scan through the command line tool, the resulting parents.mk config files will be migrated into your hosts configuration during the update process. However, only parent scan configurations on the central site will be migrated, remote site parents.mk configuration files will just be ignored. If this affects your setup, please re-trigger a parent scan for the affected child hosts in the GUI or REST API.

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