Upload an attachment for a note

Upload a file (PDF, DOCX, image, etc.) to be referenced from a note. Returns a hashed <code>attachmentId</code> — pass it in <code>attachmentIds[]</code> on POST /v1/notes. Maximum file size is 20 MB.

<strong>Content-Type</strong>: <code>multipart/form-data</code> with a single <code>file</code> field.