Suggestion - Support Headers for Attachments

[AluminumAngel]

• Flask-Mailman version: 1.0.0
• Python version: 3.11.6
• Operating System: Ubuntu 20.04.6 LTS

Description

I would like to attach an image file and embed it in the email body. To do so, I need to give the attachment a Content-ID in its header.
I cannot find a way to a header to an attachment. In Flask_Mail, this is done via an optional headers parameter passed to the attach function.