Chore: General notification reformatting (#3182)

- I unified where in file the name of `NotificationProvider.name` is placed
- I made sure that all the providers adhere to the signature of `NotificationProvider.send()`
- I made sure that all the providers use `okMsg` if returning success messages directly from the function.
  Here a discussion should be had:
  Should this be refactored into a constant of `NotificationProvider`? I could imagine that `NotificationProvider.SENDING_SUCCESSFULL`  could be a suitable alternative.
- I made sure all providers have the URL they `POST`/`GET` to be extraced into a variable.
  => refactored this way due to Nelsons suggestion

server/notification-providers/pushdeer.js

@@ -3,17 +3,15 @@ const axios = require("axios");
 const { DOWN, UP } = require("../../src/util");
 
 class PushDeer extends NotificationProvider {
-
     name = "PushDeer";
 
     /**
      * @inheritdoc
      */
     async send(notification, msg, monitorJSON = null, heartbeatJSON = null) {
-        let okMsg = "Sent Successfully.";
-        let endpoint = "/message/push";
-        let serverUrl = notification.pushdeerServer || "https://api2.pushdeer.com";
-        let pushdeerlink = `${serverUrl.trim().replace(/\/*$/, "")}${endpoint}`;
+        const okMsg = "Sent Successfully.";
+        const serverUrl = notification.pushdeerServer || "https://api2.pushdeer.com";
+        const url = `${serverUrl.trim().replace(/\/*$/, "")}/message/push`;
 
         let valid = msg != null && monitorJSON != null && heartbeatJSON != null;
 
@@ -34,7 +32,7 @@ class PushDeer extends NotificationProvider {
         };
 
         try {
-            let res = await axios.post(pushdeerlink, data);
+            let res = await axios.post(url, data);
 
             if ("error" in res.data) {
                 let error = res.data.error;