Rollout C8 templates support

[pinussilvestrus]

What should we do?

In order to make new C8 templates available, we have to add the cloud-element-templates provider to the Cloud Bpmn Editor (via camunda-bpmn-js). Since we have now two types of element templates, we need to make sure we only add correct element templates to the respective tab (C7 templates for platform, C8 templates for cloud, cf. bpmn-io/bpmn-js-properties-panel#561)

Components we need to touch

• CloudBpmnEditor (load templates, distinguish with platform templates)
• features/applyDefaultTemplates
• ElementTemplatesModal (display for cloud as well)
• CloudConnect Plugin (verify it does not explode)

Why should we do it?

Make C8 templates available.
Child of #2640

[pinussilvestrus]

ElementTemplatesModal (display for cloud as well)

I just noticed that the modal is built as a bpmn-js plugin, hooking into bpmn.modeler.configure and adding certain extensions.

So, adding this for cloud-bpmn is basically blocked by https://github.com/bpmn-io/internal-docs/issues/425, making it possible to hook into the same events for cloud tabs (/cc @Skaiir ).