Add HCI support

[dhalbert]

Goes with adafruit/circuitpython#3310.

Add code to initialize a Bluetooth HCI adapter. The current pins should work for the on-board adapter on Metro M4 AirLift, PyPortals, and PyBadge AirLift.

[EDITED]

For an onboard adapter using standard pins:

from adafruit_ble import BLERadio
from adafruit_airlift.esp32 import ESP32

esp32 = ESP32()
adapter = esp32.start_bluetooth()
ble = BLERadio(adapter)

For an offboard AirLift breakout, which will use different pins, the kind of code below works:

import board
import busio
from adafruit_ble import BLERadio
from adafruit_airlift.esp32 import ESP32

# Sample offboard pins: could be different.
esp32 = ESP32(
    reset=board.D12,
    gpio0=board.D10,
    busy=board.D11,
    chip_select=board.D13,
)

# Bluetooth needs a UART for communication.
uart = busio.UART(board.TX, board.RX, baudrate=115200, timeout=0, receiver _buffer_size=512)
adapter = esp32.start_bluetooth(uart=uart)
ble = BLERadio(adapter)

[tannewt]

Looks good! Thanks!