[Feature Request] Add picture support for "Post DE"

[niwi-hh]

Environment:
Home Assistant version: 2025.1.4
Mail and packages 0.4.2

Describe the feature request:
I use this integration for the German service "Post DE". "Post DE" is a service for shipping mails, not packages. The e-mails scanned for "Post DE" not only inform about a soon to delivered mail but also include a scan of the envelope. It would be a nice feature if this could be used by this integration. For example, I would like to integrate these pictures in a dashboard.

The image is included in the mail source after this text block:

------=_Part_2483873_704813921.1738119599601
Content-Type: image/png
Content-Transfer-Encoding: base64
Content-Disposition: inline
Content-ID: <Umschlag_20250129_03-59.png>

[sebpless]

This feature will be a gamechanger for me!