The Search in the Title Record Link Tab does not search in parent processes only

[BartChris]

Is your feature request related to a problem? Please describe.
When searching in the Title Record Link Tab for processes which the to be created process should be linked to, Kitodo is not limiting the search to processes which qualify as parents. Instead all the processes are searched which is probably not what the user wants since he or she cannot link them.

To only find the parent one has to give the precise identifier

Describe the solution you'd like
The search should - if possible - return only processes which qualify as possible parent processes.

Additional context
This issue came up while discussing necessary changes to the parent link process in #5869