Feature Request: X-priority icons

Expected behavior

Tell us what should happen
X-Priority: 1 should result in a red exclamation in the email listing
X-Priority: 5 should result in a blue downwards pointing arrow in the email listing.

Actual behavior

Tell us what happens instead
Theres no icons for X-priority

Steps to reproduce

1. Receive an email with X-priority
2. Notice it has no priority icons

It might be undesirable for some users to have such icons, as some spam does include these headers, why I suggest it being a configuration thing.

(I have for example configured my email server to delete the originating X-Priority header, and then set X-Priority: 1 and X-Priority: 5 depending on the result of the SPF lookup, so I can at a glance see if the email is either passed (no icon), neutral/none (red exlamation mark), temperr/permerr (blue downarrow).
(failed messages softfail/hardfail are outright rejected)

In this way, I can at a glance know if the email is something to trust, if my bank sends a email with a red exclamation mark, I know its fishy, but if it has no icon, I know I can trust links and attached things.

Environment

K-9 Mail version:
5.708

Android version:
10

Account type (IMAP, POP3, WebDAV/Exchange):
IMAP

Start by tracing the email listing and the handling of X-Priority headers in the Android app. Define how priorities 1 and 5 map to icons, where users can enable or disable them, and test that the configured listing shows the expected indicators without a header showing none.