Closes #1184

Code Changes

• Modified SaaSConfig.get_graph() to add a placeholder field that assists with graph traversal when a delete request is defined without a read request
• Modified SaaSConnector.retrieve_data() to return a single empty dictionary [{}] in the event of a delete-only endpoint to still be able to trigger SaaSConnector.mask_data()
• Updated the SaaS config tests
• Updated the SaaS connector tests

Steps to Confirm

• Covered by unit tests

Pre-Merge Checklist

• All CI Pipelines Succeeded
• Documentation Updated:
  • documentation complete, or draft/outline provided (tag docs-team to complete/review on this branch)
  • documentation issue created (tag docs-team to complete issue separately)
• Issue Requirements are Met
• Relevant Follow-Up Issues Created
• Update CHANGELOG.md

Description Of Changes

Updates the dataset that is generated from a SaaS config. Originally, we used the param_values of a read request to generate the collections and the identity/dataset references. We needed to support the use case where an endpoint only has a delete request defined and we don't have a read request to build the collection from. This approach flags the first generated field as a primary_key to make sure the delete-only collection is still visited during graph traversal. This solution will need to be revisited when we no longer need to flag a field as a primary_key to call the erasure on a collection (#1199).