Attachment meta data not syncing

Currently, the attachment post type is not synced. When an attachment needs to be pushed a new attachment is created on the portal site, and attached to the pushed post that needs it.

There are two ways to make sure all attachment meta data is pushed across...

**1. Push the attachment post type**

To do this we'd need to find a way to check if we actually _need_ to push the attachment to the portal (i.e. is it on a pushed post/being pushed?) otherwise each portal will end up with every attachment from every source site pushed to it, which is unnecessary and soaks up disk space.

**2. Copy attachment meta data**

This way, we still create attachments only when needed but add the meta data. However, we'd then need a task to update that meta data if the source attachment changes. The easy solution to that is to sync the attachment post type, but that has it's own issues.

_Needs more thought_