Add support for keeb.io fourier split keyboard (#1056)

* Add support for keeb.io fourier

* Update app/boards/shields/fourier/fourier_right.overlay

Co-authored-by: Nick Winans <nick@winans.codes>

* Update app/boards/shields/fourier/fourier_left.overlay

Co-authored-by: Nick Winans <nick@winans.codes>

* Convert spaces to tabs in .dtsi

Co-authored-by: Nick Winans <nick@winans.codes>

app/boards/shields/fourier/fourier.zmk.yml

@@ -0,0 +1,12 @@
+file_format: "1"
+id: fourier
+name: Fourier Rev. 1
+type: shield
+url: https://github.com/keebio/fourier
+requires:
+  - pro_micro
+features:
+  - keys
+siblings:
+  - fourier_left
+  - fourier_right