Flowable-rest module add/delete multiple instances execution API does not exist

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Flowable-rest module add/delete multiple instances execution API

In flowable-engine Include **runtimeService.addMultiInstanceExecution** and **runtimeService.deleteMultiInstanceExecution** function.

```
public Execution addMultiInstanceExecution(String activityId, String parentExecutionId, Map executionVariables) {
return (Execution)this.commandExecutor.execute(new AddMultiInstanceExecutionCmd(activityId, parentExecutionId, executionVariables));
}

public void deleteMultiInstanceExecution(String executionId, boolean executionIsCompleted) {
this.commandExecutor.execute(new DeleteMultiInstanceExecutionCmd(executionId, executionIsCompleted));
}
```

Hope to receive support in flowable-rest module.