Add hotkey to close Helix from within the initial file picker

[eulores]

When I open Helix with a directory and therefore land in the file picker I would like to quickly close it again and return to the calling application.
This is typically needed when reviewing PKGBUILDS during SW installation on Arch linux.

The default keys only include ESC (or Ctrl-C) to return back to Helix normal mode where I can then press yet another key combination of my choosing to close the editor.

I suggest to include Ctrl-Q to close down the editor from within the picker. This would only work if no open buffers had unsaved changes. A better option is to start supporting key remapping :-)

Related to #5505