Support Element Templates for Camunda Cloud BPMN diagrams

[MaxTru]

This is an epic issue that may be broken down into multiple tasks if needed

Is your feature request related to a problem? Please describe.

Support Element Templates for Camunda Cloud BPMN diagrams following the same concept as exists for Camunda Platform BPMN diagrams. (c.f. element template docs)

Describe the solution you'd like

• Use the same concept as we have (c.f. docs)
• In the first step, support
  • zeebe:taskDefinition (String, Dropdown or Hidden binding + support for constraints)
  • zeebe:taskHeader (String, Dropdown or Hidden binding + support for constraints)
  • zeebe:input(String, Dropdown or Hidden binding + support for constraints)
  • zeebe:output (String, Dropdown or Hidden binding + support for constraints)
• Consider an overall flag for an element template to indicate for which execution platform they are valid
• To consider / cherry-on-top: optional attribute => Don't inject configurations using element templates, if user provides no value bpmn-io/bpmn-js-properties-panel#501 (comment)

Breakdown

• Add element templates support for Connectors story bpmn-io/bpmn-js-properties-panel#540
• Add ability to create optional inputs & outputs via cloud element templates bpmn-io/bpmn-js-properties-panel#559
• Make it possible to structure element templates in sections #2673
• Learn from first user story and make element templates a platform agnostic feature (C7 vs. C8)
  • Implement JSON Schema and Validator for C8 templates bpmn-io/bpmn-js-properties-panel#561
  • Consider restructuring of element templates providers bpmn-io/bpmn-js-properties-panel#562
• Rollout C8 templates support #2731
• Update element template docs #2723
• Track cloud element templates usage via ET #2786
• Consider (bpmn.io) blog post for cloud-element-templates => cf. bpmn-io/internal-docs#403 (comment)

Describe alternatives you've considered

• Re-build a new concept => does not make sense. Element templates concept as-is works fine.
• ...

Additional context

Also see archived zeebe-modeler issue zeebe-io/zeebe-modeler#119
Related to https://github.com/camunda/product-hub/issues/2
Element templates docs

There does not exist a dedicated BPMN extension element reference for Zeebe. The examples should be used as a reference.

[pinussilvestrus]

Another thing that might be important for the Connectors story after a chat with @nikku and @pihme (maybe not in the first iteration)

• Inputs and outputs are also relevant
• Inputs and outputs support dynamic binding ("=expression") or static values ("1") => that might conclude in another type "Expression" if we decide to provide additional editor tooling around it

In general, the existing templates concept fits well with what we need for the Connectors story, although there are unclarified things regarding the connection of a template and a connector implementation (top-down vs. bottom-up). Either way, we can start with the way element templates are currently working.

[pinussilvestrus]

Let's close this one as all implementation tasks are done. To consider: https://github.com/bpmn-io/internal-docs/issues/403#issuecomment-1057771316