[Keyboard] Keyboardio Atreus (#10570)

* Initial support for the Keyboardio Atreus

Many thanks to noroadsleft for reviews & suggestions.

* Add QMK Configurator layout support

* Update the fn layer of the Keyboardio Atreus to the new layout.

Previously this was using the Classic Atreus layout.

* Implement noroadleft's changes from #8492

* Follow Erovia's recommendations

qmk/qmk_firmware#8492

* Correct braces

* Change correct rules.mk

* Remove comments

* Fix BOOTMAGIC_ENABLE

I had edited the wrong file earlier.

* Remove comment

* Updates rules.mk

Thank you noroadsleft.

Co-authored-by: Gergely Nagy <algernon@keyboard.io>
Co-authored-by: Phil Hagelberg <phil@hagelb.org>

keyboards/keyboardio/atreus/rules.mk

@@ -0,0 +1,24 @@
+# MCU name
+MCU = atmega32u4
+
+# Bootloader selection
+BOOTLOADER = caterina
+
+# Build Options
+#   change yes to no to disable
+#
+BOOTMAGIC_ENABLE = lite     # Virtual DIP switch configuration
+MOUSEKEY_ENABLE = yes       # Mouse keys
+EXTRAKEY_ENABLE = yes       # Audio control and System control
+CONSOLE_ENABLE = yes        # Console for debug
+COMMAND_ENABLE = yes        # Commands for debug and configuration
+# Do not enable SLEEP_LED_ENABLE. it uses the same timer as BACKLIGHT_ENABLE
+SLEEP_LED_ENABLE = no       # Breathing sleep LED during USB suspend
+# if this doesn't work, see here: https://github.com/tmk/tmk_keyboard/wiki/FAQ#nkro-doesnt-work
+NKRO_ENABLE = yes           # USB Nkey Rollover
+BACKLIGHT_ENABLE = no       # Enable keyboard backlight functionality
+RGBLIGHT_ENABLE = no        # Enable keyboard RGB underglow
+BLUETOOTH_ENABLE = no       # Enable Bluetooth
+AUDIO_ENABLE = no           # Audio output
+
+UNICODE_ENABLE = yes        # Unicode