Support for forwarding services headers

Is your feature request related to a problem? Please describe.
I use SimpleLogin, which helps me more easily create one email alias per service. Because of this, my emails all look like they come from email addresses like reply+iwehobhuhuoeahfewouhb@simplelogin.co instead of the forwarded address.

Describe the solution you'd like
SimpleLogin adds several headers to each email, allowing you to see the original sender:

https://github.com/simple-login/app/blob/ee0ed7d9ec822bcd5355c0d61930aa0f1ddccdb0/app/email/headers.py#L27-L30

For example:

X-SimpleLogin-Envelope-From: noreply@github.com
X-SimpleLogin-Envelope-To: my_alias@example.com

It would be great if K-9 Mail could use these headers to display the from and to address that the emails are forwarded from.

Describe alternatives you've considered
Another option would be perhaps to talk to the SimpleLogin app, but this seems more complex and also harder to extend to other forwarding services like AnonAddy.

Additional context
This should probably be something the user should enable manually (something like Email -> Forwarding Service -> SimpleLogin), to prevent malicious emails using such headers to spoof.

Start by reviewing the SimpleLogin reference at app/email/headers.py lines 27-30 to understand the forwarding headers and compare the proposal with AnonAddy. Then trace K-9 Mail's message-address display and account settings entry points. Done means configured forwarding services can show the forwarded sender and recipient without treating untrusted headers as authoritative by default.