code: public <R1> TransactionFlow<T,R1> flatMap(Function<R,TransactionFlow<T,R1>> fn){
  		return of(transactionTemplate,a -> fn.apply(transaction.apply(a)).transaction.apply(a));
  	}
docs: Transform data in the context of a Transaction and optionally propgate to / join with a new TransactionalFlow
  * <pre>
  {code
  String result = TransactionFlow.of(transactionTemplate, this::load)
  .flatMap(this::newTransaction)
  .execute(10)
  .get();
  }
  </pre>
  
  
  @param fn flatMap function to be applied
  @return Next stage in the transactional flow