feat(shields): Reviung34 shield definition

* Initial implementation of REVIUNG34 shield.
* Add copyright information to files
* Added a README with instructions on how to enable the 1x2u layout.
* Add a default chosen matrix transform in the default keymap, alongside a commented out version for the alternate layout.

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Co-authored-by: Peter Johanson <peter@peterjohanson.com>
Co-authored-by: Cem Aksoylar <caksoylar@users.noreply.github.com>

app/boards/shields/reviung34/reviung34.zmk.yml

@@ -0,0 +1,9 @@
+file_format: "1"
+id: reviung34
+name: REVIUNG34
+type: shield
+url: https://github.com/gtips/reviung/tree/master/reviung34
+requires: [pro_micro]
+features:
+  - keys
+  - underglow