Reintroduce 'ROOTAPI' so domain and protocol can be configured

eg. setter for api root added as comment in examples/BASIC/BASIC.ino

examples/BASIC/BASIC.ino

@@ -126,6 +126,9 @@ void setup() {
   openMetrics.setAirGradient(&ag);
   localServer.setAirGraident(&ag);
 
+  /** Example set custom API root URL */
+  // apiClient.setApiRoot("https://example.custom.api");
+
   /** Init sensor */
   boardInit();