Rich text attachments

Rich text fields are used in many parts of the API, usually indicated by fields with a "_html" suffix.

Attaching an image or file to a rich text field

1. Upload the attachment
2. Record the data.file.attachable_sgid reference from the response
3. In the rich text body, include:

<action-text-attachment sgid="abc123"></action-text-attachment>

Retrieving an attachment referenced in a rich text field

1. Fetch the HTML content of the rich text field
2. Determine the SGID of the attachment from the HTML
3. Retrieve the attachment details via the API
4. Download the attachment file from the file.file_url field provided by the API response