Add UptimeRobot API key validation check

Author: andrewmumblebee

plugins/UptimeRobot/v2/configValidation.json

@@ -0,0 +1,11 @@
+{
+  "steps": [
+    {
+      "displayName": "API access",
+      "dataStream": { "name": "monitors" },
+      "success": "Successfully connected to API",
+      "error": "Can't access API, please check your UptimeRobot API key and permissions",
+      "required": true
+    }
+  ]
+}