Add 'downloadOTA' command to download OTA file and verify length/CRC

[aentinger]

Test sketch ...

#include <WiFiNINA.h>

void setup() {

  Serial.begin(115200);
  while (!Serial) { }
  
  int status = WL_IDLE_STATUS;
  do {
    status = WiFi.begin("SSID", "PASS");
    delay(5000);
  } while ( status != WL_CONNECTED);

  /* Download new files. */
  if (!WiFiStorage.downloadOTA("https://downloads.arduino.cc/test/wifi1010-sha256-remote.ota")) {
    Serial.println("WiFiStorage.downloadOTA(...) error");
    return;
  }
  Serial.println("Download complete");

  /* Read length. */
  len = 0;
  if (WiFiStorage.exists("/fs/UPDATE.BIN.LZSS", &len)) {
    Serial.print("File size = ");
    Serial.println(len);
  } else {
    Serial.println("WiFiStorage.open(...) error");
  }
}

void loop()
{

}

Related PRs:

• Add 'downloadOTA' command to download OTA file and verify length/CRC arduino/nina-fw#53
• Adapt SNU for Nina-HTTPS-OTA download. arduino/ArduinoCore-samd#553