addMultiInstanceExecution method support batch operations

**Is your feature request related to a problem? Please describe.**

If I want to add many instances, calling the addMultiInstanceExecution method in the loop will be slow and have performance problems. I try to call this method in multiple threads at the same time, but prompting FlowableOptimisticLockingException.

**Describe the solution you'd like**

Can the addMultiInstanceExecution method be enabled to support batch operations, which can reduce call time and improve efficiency.thanks.

**Describe alternatives you've considered**

A clear and concise description of any alternative solutions or features you've considered.

**Additional context**

Add any other context or screenshots about the feature request here.
Models, if applicable, always help to clarify a problem. Ideally, a unit test makes reproducing things easier.