feat: Add a few sample hardware metadata files.

app/boards/arm/bdn9/bdn9_rev2.zmk.yml

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+file_format: "1"
+id: bdn9_rev2
+name: BDN9 Rev2
+type: board
+arch: arm
+outputs:
+  - usb
+features:
+  - keys
+  - encoder
+url: https://keeb.io/collections/bdn9-collection/products/bdn9-rev-2-3x3-9-key-macropad-rotary-encoder-and-rgb

app/boards/arm/nrfmicro/nrfmicro_11.zmk.yml

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+file_format: "1"
+id: nrfmicro_11
+name: nRFMicro 1.1/1.2
+type: board
+arch: arm
+outputs:
+  - usb
+  - ble
+url: https://github.com/joric/nrfmicro/
+exposes: [pro_micro]

app/boards/arm/nrfmicro/nrfmicro_11_flipped.zmk.yml

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+file_format: "1"
+id: nrfmicro_11_flipped
+name: nRFMicro 1.1 (flipped)
+type: board
+arch: arm
+outputs:
+  - usb
+  - ble
+url: https://github.com/joric/nrfmicro/
+exposes: [pro_micro]

app/boards/arm/nrfmicro/nrfmicro_13.zmk.yml

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+file_format: "1"
+id: nrfmicro_13
+name: nRFMicro 1.3/1.4
+type: board
+arch: arm
+outputs:
+  - usb
+  - ble
+url: https://github.com/joric/nrfmicro/
+exposes: [pro_micro]

app/boards/interconnects/pro_micro/pro_micro.zmk.yml

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+file_format: "1"
+id: pro_micro
+name: Pro Micro
+type: interconnect
+url: https://www.sparkfun.com/products/12640
+manufacturer: SparkFun
+description: |
+  The SparkFun Pro Micro grew popular as a low cost ATmega32U4 board with sufficient GPIO and peripherals
+  to work for many keyboard needs. Since the original Pro Micro, many pin compatible boards have appeared,
+  with various changes or improvements, such as the Elite-C w/ USB-C, nice!nano with nRF52840 wireless.

app/boards/shields/corne/corne.zmk.yml

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+file_format: "1"
+id: corne
+name: Corne
+type: shield
+url: https://github.com/foostan/crkbd/
+requires: [pro_micro]
+exposes: [i2c_oled]
+features:
+  - keys
+  - display
+siblings:
+- corne_left
+- corne_right