Support Escalation Triggers for External Tasks

[ThorbenLindhauer]

This issue was imported from JIRA:

Field	Value
JIRA Link	CAM-12847
Reporter	@mboskamp
Has restricted visibility comments	false

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CAM-12040 introduces errorEventDefinitions with expressions that trigger throwing of a BPMN error when resolved to true.
The same functionality can be used for escalations that trigger based on an expression.

The only notable difference is that escalation events can be non-interrupting. In this case, the current activity is not canceled. In every other sense, it should behave similarly to throwing a BPMN error through an error trigger.

Links:

• is related to https://jira.camunda.com/browse/CAM-12040