Introduce possibility to disable task related content uploads (not using a task form) for a process

Summary
A user task, which does not have a form currently offers possibility to attach task related content via "Add a document and share the knowledge" (see attached taskRelatedContent.png). This option is even available in tasks with a referenced form by clicking on "task details". Customer would like to disable this functionality per configuration, as their APS users shall only attach content when the user task form has an attach field.

Steps to reproduce
1. In activiti-app, create a new process in BPMN editor via App designer
2. Process shall have start event->user task (without form)-> end event
3. Save the process and publish an app containing the process
4. From the published app start a new process
5. Inspect the available options in the user task

Current behaviour
A user task offers the ability to "Add a document and share the knowledge"

Desired behaviour
There should be no way from the default UI to attach task related content, other than using a task form with an attach field. This option shall be configurable, as other customers might need that functionality and are already used to it.

Business case
Customer would like the ability to disable task related attachments, as their users shall only upload content to a process via and attach form field from the app UI. One reason for this request is also enhancement request MNT-19555