Unable to remove prefixes/suffixes that are currently used by an existing orders

Overview

Following UIOR-496 it's we want to add restrictions to which poNumber prefixes/suffixes can be deleted.

When deleting an already configured prefix or suffix, check for any orders with that prefix/suffix. If any exist, do not perform the delete and return an appropriate error message

Background

This will help avoid confusing situations where an order is created with a given prefix/suffix, and the user wants to edit the poNumber for that order at some later time, only to find that the prefix doesn't appear in the drop-down because it's been removed between in the time between order creation and edit.

Note : With an increase in the number of orders, the time required to verify the existence of orders will increase.

Acceptance Criteria

Logic added to check for existing orders with suffixes/prefixes and return error if orders exist
Unit test updated
API test updated