[Receipts] Inline attachments don't get rendered properly

### Describe your goals

We should pass attachments into WickedPdf somehow. One option would be to find and replace `cid:#{attachment.content_id}` with a base64 representation of the image.

### Describe the bug

When you paste an image into an email and send it to `receipts@hcb.gg`, the inline image doesn't get rendered. This is because we don't pass that information into `WickedPdf`.