[docs]: create callback clarification for replay

### URL/Location

https://docs.aws.amazon.com/durable-execution/sdk-reference/operations/callback/#wait-for-external-systems

### Describe What's Incorrect or Lacking

Better describe effect of replay on createcallback - i.e that you have to wrap your submitter code in a step and the consequences of not doing so (submitter code will run again on replay if not in durable operation).

### Suggested Improvement

_No response_

### Additional Context

_No response_