Add mbed_app configuration to use MTxDot with Lora

[Copper-Bot]

The Lora configuration could be add in this repository to help user configure the zest core MTxDOT with Lora.

It could be either a mbed_app.json template file directly in the repo, or describe the setup in the Readme.

"ZEST_CORE_MTXDOT": {
            "target.components_add":             ["SX1272"],
            "sx1272-lora-driver.spi-mosi":        "LORA_MOSI",
            "sx1272-lora-driver.spi-miso":        "LORA_MISO",
            "sx1272-lora-driver.spi-sclk":        "LORA_SCK",
            "sx1272-lora-driver.spi-cs":          "LORA_NSS",
            "sx1272-lora-driver.reset":           "LORA_RESET",
            "sx1272-lora-driver.dio0":            "LORA_DIO0",
            "sx1272-lora-driver.dio1":            "LORA_DIO1",
            "sx1272-lora-driver.dio2":            "LORA_DIO2",
            "sx1272-lora-driver.dio3":            "LORA_DIO3",
            "sx1272-lora-driver.dio4":            "LORA_DIO4"
}