Allow multiple network SSIDs to be defined within secrets.json file

[brentru]

Allow for multiple SSIDs to be defined within secrets.json, by priority

"network_type_wifi":[
          {
		"network_ssid":"my_house",
		"network_password":"password"
	},
        {
		"network_ssid":"the_garden",
		"network_password":"password"
	}
]

via @tyeth on #328 (comment)

I think long term I'd love the support of single object and/or array for networks, and to potentially add a key for priority, or potentially just use RSSI based priority upon start/disconnect. i.e. currently it's:

[isomorphic85]

YES, this would be amazing

[brentru]

This should be simple with the new WiFiMulti library inside BSP 3.x

https://docs.espressif.com/projects/arduino-esp32/en/latest/api/wifi.html#wifimulti

[brentru]

@tyeth Want to tackle this one next week?

[tyeth]

This has been added under the new additional key of alternative_networks.

Please see this playground note for details:
https://adafruit-playground.com/u/tyeth/pages/using-multiple-wifi-network-credentials-in-adafruit-io-wippersnapper-firmware