Missing variable reader for external tasks

[FlorianCassayre]

Scenario

• camunda-bpm-data version: 1.2.8
• Camunda BPM version: 7.17.0
• Description of your use case: there is no reader for external tasks

Current Behaviour

ExternalTask externalTask = ...;
VariableReader reader = reader(externalTask.getAllVariablesTyped());
var value = reader.get(MY_VARIABLE);

Wanted Behaviour

VariableReader reader = reader(externalTask); // No call to getAllVariablesTyped

Possible Workarounds

See Current Behaviour. It's not convenient to call getAllVariablesTyped on the external task, this should be abstracted by the library. Reading variables from external tasks is a common use case (see the ExternalTaskHandler interface).

[zambrovski]

Must be implemented in a new additional module, since it depends on external-client which is not part of the c7 engine.