Add rule for exclusive=false

[falko]

see also camunda/camunda-modeler#1501

[nikku]

If we implement this the rule should go to camunda/bpmnlint-plugin-camunda#3.

Can you provide some background information in camunda/bpmnlint-plugin-camunda#3:

• Should it be an error or warning per default
• How should the documentation look like? We need a description why this is a problem.

[nikku]

Closing this as it is moved to camunda/bpmnlint-plugin-camunda#3.

[falko]

It should be a warning by default. exclusive=true allows the Job Executor to execute jobs from the same process instance with multiple threads. This is generally not advisable and can cause problems, e.g. with parallel variable access.