Since request.Body can only be read once, calling patchUser from
patchSelf always returned an error. request.Body needed to be either be
saved in a variable and reset or have a new function created.
Uses gift package for server side resizing of selected letterhead
file. It should fit an image file with aspect ratio of 2:1 and be a
reasonable size. A 400x200 resizeToFit is used for now.
gift just uses the native image/draw package internally.
https://pkg.go.dev/image/draw