Add keyboard shortcuts for Elgato key lights

- create Gnome keyboard shortcuts to manage the Elgato key lights:
  + toggle
  + increase and decrease brightness
- we use Python scripts in ~/.config/gnome-settings/elgato
  based on the "leglight" PIP package
  (Source: https://gitlab.com/obviate.io/pyleglight)

.config/gnome-settings/elgato/README.md

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+# Elgato Key Lights
+
+The Python files in this folder are hooked as keyboard shortcuts in Gnome.
+They allow to toggle the key lights in my office.
+In the long-run, these scripts should be improved a bit.

.config/gnome-settings/elgato/dec_brightness.py

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+#!/usr/bin/env python
+
+import leglight
+
+LEFT_KEYLIGHT_IP = "192.168.20.72"
+RIGHT_KEYLIGHT_IP = "192.168.20.73"
+
+left = leglight.LegLight(LEFT_KEYLIGHT_IP, port=9123)
+right = leglight.LegLight(RIGHT_KEYLIGHT_IP, port=9123)
+
+left.decBrightness(5)
+right.decBrightness(5)

.config/gnome-settings/elgato/inc_brightness.py

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+#!/usr/bin/env python
+
+import leglight
+
+LEFT_KEYLIGHT_IP = "192.168.20.72"
+RIGHT_KEYLIGHT_IP = "192.168.20.73"
+
+left = leglight.LegLight(LEFT_KEYLIGHT_IP, port=9123)
+right = leglight.LegLight(RIGHT_KEYLIGHT_IP, port=9123)
+
+left.incBrightness(5)
+right.incBrightness(5)

.config/gnome-settings/elgato/toggle_keylights.py

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+#!/usr/bin/env python
+
+import leglight
+
+LEFT_KEYLIGHT_IP = "192.168.20.72"
+RIGHT_KEYLIGHT_IP = "192.168.20.73"
+
+left = leglight.LegLight(LEFT_KEYLIGHT_IP, port=9123)
+right = leglight.LegLight(RIGHT_KEYLIGHT_IP, port=9123)
+
+if left.info()["on"] or right.info()["on"]:
+    left.off()
+    right.off()
+
+else:
+    left.on()
+    right.on()
+    left.brightness(30)
+    right.brightness(30)
+    left.color(6000)
+    right.color(6000)