batches: Debug message when namespace deleted

Created by: Piszmog

Closes #39723 (closed).

When calling GetBatchChange, removed the requirement to that the org and user deleted_at be null. Instead, during the scan call, setting the deleted_at values into 2 variables. If these variables are not "zero," then a new error (ErrDeletedNamespace) is returned to signify that the namespace has been deleted.

With this error, we can now check if the error is ErrDeletedNamespace and log a debug message saying that the changeset is being skipped.

Test plan

Added Go Unit Tests