feat(shields): Microdox V2 shield definition

* Refactor common parts of the Microdox sheild into a separate file. This is in preparation for adding Microdox V2 as another shield in the same directory.
* Refactor Microdox keymap into a common file in preparation for Microdox V2
* Add Microdox V2 shield definition
* Added a README to explain v1/v2 differences.

app/boards/shields/microdox/microdox_common.dtsi

@@ -0,0 +1,51 @@
+/*
+ * Copyright (c) 2023 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <dt-bindings/zmk/matrix_transform.h>
+
+/ {
+    chosen {
+        zephyr,display = &oled;
+        zmk,kscan = &kscan0;
+        zmk,matrix_transform = &default_transform;
+
+    };
+
+    default_transform: keymap_transform_0 {
+        compatible = "zmk,matrix-transform";
+        columns = <10>;
+        rows = <4>;
+// | SW1  | SW2  | SW3  | SW4  | SW5  |   | SW5  | SW4  | SW3  | SW2  | SW1  |
+// | SW6  | SW7  | SW8  | SW9  | SW10 |   | SW10 | SW9  | SW8  | SW7  | SW6  |
+// | SW11 | SW12 | SW13 | SW14 | SW15 |   | SW15 | SW14 | SW13 | SW12 | SW11 |
+//               | SW16 | SW17 | SW18 |   | SW18 | SW17 | SW16 |
+        map = <
+RC(0,0) RC(0,1) RC(0,2) RC(0,3) RC(0,4)  RC(0,5) RC(0,6) RC(0,7) RC(0,8) RC(0,9)
+RC(1,0) RC(1,1) RC(1,2) RC(1,3) RC(1,4)  RC(1,5) RC(1,6) RC(1,7) RC(1,8) RC(1,9)
+RC(2,0) RC(2,1) RC(2,2) RC(2,3) RC(2,4)  RC(2,5) RC(2,6) RC(2,7) RC(2,8) RC(2,9)
+                RC(3,2) RC(3,3) RC(3,4)  RC(3,5) RC(3,6) RC(3,7)
+        >;
+    };
+
+    // TODO: per-key RGB node(s)?
+};
+
+&pro_micro_i2c {
+    status = "okay";
+    oled: ssd1306@3c {
+        compatible = "solomon,ssd1306fb";
+        reg = <0x3c>;
+        label = "DISPLAY";
+        width = <128>;
+        height = <32>;
+        segment-offset = <0>;
+        page-offset = <0>;
+        display-offset = <0>;
+        multiplex-ratio = <31>;
+        com-sequential;
+        prechargep = <0x22>;
+    };
+};