We currently have redundant enums for the types of change streams in our pipeline code:

• change_stream.h
• document_source_change_stream.h

To simplify this, we should remove the one in document_source_change_stream.h and use the one from change_stream.h instead.
Going forward, we should however change the enum value names in change_stream.h to the more expressive names in document_source_change_stream.h.