Support zeebe:property for templating

[nikku]

Is your feature request related to a problem? Please describe

We want to support templating for the generic zeebe:property BPMN extension.

By doing so we open a wide range of use-cases for users to build re-usable building blocks where configurating is not important to Zeebe, but to external systems (i.e. inbound connectors).

Describe the solution you'd like

• I can bind a template property to zeebe:property in a way I can bind to zeebe:input
• optional is supported, i.e. optional zeebe:property binding is only serialized if it is user (or default value) defined

Describe alternatives you've considered

None.

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Depends on camunda/zeebe-bpmn-moddle#30
Depends on camunda/element-templates-json-schema#65
Related to camunda/camunda#9868
Related to https://github.com/camunda/product-hub/issues/335

[christian-konrad]

Currently no time in this iteration, moving into 'backlog' to be picked up later.

[menski]

FYI the Zeebe part was implemented with camunda/camunda#9955, and will be released with 8.1.0-alpha5 beginning of September, but can already be tested with the latest SNAPSHOT

[nikku]

Picking this up myself to work on it next week.

[PreetiNirwal]

Thanks @philippfromme!