[Keyboard] Add handwired BDN9-BLE (#8192)

* Add handwired BDN9-BLE

* Apply suggestions from code review

Co-Authored-By: Ryan <fauxpark@gmail.com>

* Update keyboards/handwired/bdn9_ble/rules.mk

Co-Authored-By: Ryan <fauxpark@gmail.com>

* Update keyboards/handwired/bdn9_ble/rules.mk

Co-Authored-By: Ryan <fauxpark@gmail.com>

* Update keyboards/handwired/bdn9_ble/readme.md

Co-Authored-By: James Young <18669334+noroadsleft@users.noreply.github.com>

Co-authored-by: Ryan <fauxpark@gmail.com>
Co-authored-by: James Young <18669334+noroadsleft@users.noreply.github.com>

keyboards/handwired/bdn9_ble/rules.mk

@@ -0,0 +1,37 @@
+# MCU name
+MCU = atmega32u4
+
+# Processor frequency
+F_CPU = 8000000
+
+# Bootloader selection
+#   Teensy       halfkay
+#   Pro Micro    caterina
+#   Atmel DFU    atmel-dfu
+#   LUFA DFU     lufa-dfu
+#   QMK DFU      qmk-dfu
+#   ATmega32A    bootloadHID
+#   ATmega328P   USBasp
+BOOTLOADER = caterina
+
+# Build Options
+#   change yes to no to disable
+#
+BOOTMAGIC_ENABLE = no      # Virtual DIP switch configuration
+MOUSEKEY_ENABLE = no       # 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 = no            # USB Nkey Rollover
+BACKLIGHT_ENABLE = yes       # Enable keyboard backlight functionality
+RGBLIGHT_ENABLE = no       # Enable keyboard RGB underglow
+MIDI_ENABLE = no            # MIDI support
+UNICODE_ENABLE = no         # Unicode
+BLUETOOTH = AdafruitBLE       # Enable Bluetooth
+AUDIO_ENABLE = no           # Audio output on port C6
+FAUXCLICKY_ENABLE = no      # Use buzzer to emulate clicky switches
+HD44780_ENABLE = no 		# Enable support for HD44780 based LCDs
+ENCODER_ENABLE = no