[Feature Request] Append printed E-mail and/or attach e-mail body to PDF attachments

Description Note: re-opening #6876 Background As per the [docs]( Paperless will "check if there are any consumable attachments" and "If so, instruct paperless to consume the attachments and optionally use the metadata provided in the rule for the new document.". This is fantastic. With the [optional services]( paperless will convert eml files. I regularly want to keep the e-mail itself, in addition to the attachments. For example: 1. I may get a PDF fax, but the e-mail itself from the fax provider has the confirmation date/time. 2. I may get a PDF receipt of a deposit, but the e-mail itself has information on what the deposit relates to 3. I may get a copy of the contract but the e-mail introduces the key points and provides a good executive summary. Typically for faxes, I have saved the PDF to a folder, then printed the e-mail and 'appended' it to the PDF as the last page. This gives me a full record of the PDF, including the date/time…