[SAP] Exit for MM release strategy at Purchase document level

 At times, business requires release strategy to be triggered for purchasing documents based on custom parameters or through internal validations.

In this case, we cannot go through the standard release strategy due to custom validations or fields. 

To accomplish this requirement, new logic need to be maintained in Customer exit: EXIT_SAPLEBND_002. 

Through this exit, we can perform changes to the communication structure.