Add keyboard incognito mode

Thanks for the great app! This is an enhancement request.

Expected behavior

Please add an option to disable the google keyboard (gboard) from learning words I use when using K9. See https://www.xda-developers.com/api-apps-keyboard-incognito-mode/ for an explanation. I believe the IME_FLAG_NO_PERSONALIZED_LEARNING API needs to be used.

Actual behavior

The google keyboard records all keystrokes/swipes in K-9.

Steps to reproduce

N/A This is an enhancement.

Environment

K-9 Mail version: 5.600

Android version: 9 (Pixel 3)

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