Support for related categories (Descendants / Ascendants)

[csandreas1]

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I'm always frustrated when I need to select a category or subcategory in a dropdown, for example I want to search doctors and also load descandants, like various doctor professions. I am limited to what the user is typing.

Describe the solution you'd like
provide an additional option in the dropdown. e.g. descendants. Descendants will be tied to the parent category. So for example, when I type doctors, then all doctors professions will be shown.

Easiest solution is to disable searching on the values. The user can type whatever he wants but not filter out words.
Another solution is to just show what the json has. For example on an ajax request we only care about the data.

Describe alternatives you've considered
None

Additional context
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