32818 add attachments

- Added attachment handling to CDTMutableDocumentRevision via the attachments property
- Depercated old attachment API in CDTDatastore+attachments.h
- Created new Attachment CRUD tests based off AttachmentCRUD.m
Is it worth updating the method documentation to explain what the replacement for the deprecated method is? Maybe a quick one-liner and then a reference to the README which can explain the details?