Allow user-defined X.509 Certificates for server authentication

Adds set_certificate and set_private_key methods to ESP32SPI to reflect the updated WiFiSSLClient in nina-fw.

• Use set_certificate and set_private_key to set your ESP32's certificate and private key. This will be used to authenticate your CircuitPython device to a server.
  • To use these methods, you must update the nina-fw version on your ESP32 Co-Processor/AirLift to version 1.4.0 or above.

To use in CircuitPython, simply install the Adafruit CircuitPython bundle.

To use in CPython, pip3 install adafruit-circuitpython-esp32spi.

Read the docs for info on how to use it.