Cant set the zf-rest controller_class from apigility UI

[weierophinney]

In https://apigility.org/documentation/modules/zf-rest
"Sub-key: controller_class (optional)
An alternate controller class to use when creating the controller service; it must extend ZF\Rest\RestController. Only use this if you are altering the workflow present in the RestController."

I want to extend the RestController in order to do some private handling of exceptions.
(modify createApiProblemFromException because the exceptions are lost there).
Actually I would like to be able to change it in the Apigility-Admin-GUI globally or at the "API" level

Thanks.

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Originally posted by @goalain at zfcampus/zf-apigility-admin#386