adds personal ploopy trackback keymap with drag scroll

Author: cwlucas41

keyboards/ploopyco/trackball/keymaps/drag_scroll_cwlucas41/config.h

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+#define PLOOPY_DRAGSCROLL_MOMENTARY 1
+#define PLOOPY_DRAGSCROLL_INVERT 1
+#define PLOOPY_DRAGSCROLL_MULTIPLIER 0.1

keyboards/ploopyco/trackball/keymaps/drag_scroll_cwlucas41/keymap.c

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+#include QMK_KEYBOARD_H
+
+
+const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
+    [0] = LAYOUT( /* Base */
+        KC_BTN1, KC_BTN3, KC_BTN2,
+          LT(1, KC_BTN4), KC_BTN5
+    ),
+    [1] = LAYOUT(
+        DRAG_SCROLL, _______, _______,
+          _______, _______
+    )
+};

keyboards/ploopyco/trackball/keymaps/drag_scroll_cwlucas41/readme.md

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+# Customized Drag Scroll keymap used by cwlucas41 for Ploopyco Trackball
+Derived from [ploopy Drag Scroll keymap](../drag_scroll/)
+
+Changes from original drag scroll keymap:
+* sets `PLOOPY_DRAGSCROLL_INVERT` so that drag scroll direction matches scroll wheel direction
+* sets `PLOOPY_DRAGSCROLL_MOMENTARY` - I find it being momentary is easier as 1. I only use it for short periods, and 2. I found it annoying that I could put it in drag scroll mode and then forget it is in that mode.
+* sets `PLOOPY_DRAGSCROLL_MULTIPLIER` to something that feels good - I found the default value made drag scroll way too sensitive to be useful for me
+* changes drag scroll chording to `BTN4 + BTN1` from `BTN5 + BTN1` - I like using my ring finger over my pinky when momentary mode is enabled
+