Support Zeebe's user task forms

[saig0]

Since Zeebe 1.0.0, user tasks and task forms are supported: https://docs.camunda.io/docs/reference/bpmn-processes/user-tasks/user-tasks#user-task-forms

The task forms are a new part of the Camunda stack and can be modeled directly in the modeler: https://docs.camunda.io/docs/product-manuals/tasklist/userguide/camunda-forms

Replace the previous task forms and form fields with the official Camunda forms. The form viewer can be integrated as described here: https://github.com/bpmn-io/form-js/tree/master/packages/form-js-viewer

[tbfly]

@saig0 Hi, will you please guide me, where to get "userTaskForm"? Now I can get "userTaskForm_id" from "customHeaders" by "io.camunda.zeebe:formKey".
But where to get "userTaskForm" content json string by "userTaskForm_id"?
Do I need to add "addProcessListener“ to get the all "process" xml content? Because the userTaskFrom content lay on:
<process ... >
...

xml node.

While in orig serverTask path, the "taskform" or "formFields" 's key and value are all lay on "customHeaders", and can handle one time by read job meta info.

[tbfly]

"But it order to read the form, we need to import the process record. The form is stored in the process extension zeebe:userTaskForm."

I will check this path, thx.
@saig0

[LingXin0]

Custom form logic can be associated with the userTaskForm_id, and the corresponding permissions can be verified, but can not be stored in the userTaskForm

[saig0]

A similar feature was implemented in the Zeebe-Play project. A contributor could adopt the relevant changes from the following PRs:

• feat: view and complete user task forms zeebe-play#61
• feat: load user tasks of process instance zeebe-play#69
• User Task Forms UI and data fetching zeebe-play#81