add ntfy support

ref https://github.com/louislam/uptime-kuma/issues/1622

server/notification-providers/ntfy.js

@@ -0,0 +1,29 @@
+const NotificationProvider = require("./notification-provider");
+const axios = require("axios");
+
+class Ntfy extends NotificationProvider {
+
+    name = "ntfy";
+
+    async send(notification, msg, monitorJSON = null, heartbeatJSON = null) {
+        let okMsg = "Sent Successfully.";
+        try {
+            if (notification.ntfyserverurl && notification.ntfyserverurl.endsWith("/")) {
+                notification.ntfyserverurl = notification.ntfyserverurl.slice(0, -1);
+            }
+            await axios.post(`${notification.ntfyserverurl}`, {
+                "topic": notification.ntfytopic,
+                "message": msg,
+                "priority": notification.ntfyPriority || 4,
+                "title": "Uptime-Kuma",
+            })
+
+            return okMsg;
+
+        } catch (error) {
+            this.throwGeneralAxiosError(error);
+        }
+    }
+}
+
+module.exports = Ntfy;