Avoid conditional event race condition with selected batch APIs

User Story (Required on creation):

To avoid synchronization via optimistic locking between batches and jobs running in a process instance, it should be possible to make batch jobs exclusive so that the job executor doesn't run them in parallel.

Functional Requirements (Required before implementation):

• The batch API RuntimeService#setVariablesAsync creates exclusive batch jobs
  • if a batch job is configured to modify a single process instance (see invocationsPerBatchJob, this is the default value)
  • so that the job setting the variables in the process instance is not executed in parallel with other exclusive jobs (e.g. async continuations)
• The batch API that will be developed for CAM-13113 behaves in the same way

Technical Requirements (Required before implementation):

• To be decided:
  • Should it be possible to toggle this behavior (e.g. users might want to have parallel execution of the batches)?
  • If yes, what is the default setting?
• This may require to store the type of entity that is modified by a batch job (process instance, external task, ...)

Limitations of Scope (Optional):

• This will only be built for the following batch APIs
  • RuntimeService#setVariablesAsync
  • The new batch API for message correlation: CAM-13113

Hints (Optional):

• Same scenario as in CAM-13762
• Besides enforcing synchronization between conflicting transactions via optimistic locking, it is possible to avoid conflicting transactions to run in parallel
• In the process engine, this is doable in the scope of one process instance with exclusive jobs (i.e. if a variable is modified in one job and a conditional event is entered in another job, the job executor ensures that they run one after the other, so the problem in CAM-13762 doesn't occur)