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/wecom.js

@@ -3,24 +3,22 @@ const axios = require("axios");
 const { DOWN, UP } = require("../../src/util");
 
 class WeCom extends NotificationProvider {
-
     name = "WeCom";
 
     /**
      * @inheritdoc
      */
     async send(notification, msg, monitorJSON = null, heartbeatJSON = null) {
-        let okMsg = "Sent Successfully.";
+        const okMsg = "Sent Successfully.";
 
         try {
-            let WeComUrl = "https://qyapi.weixin.qq.com/cgi-bin/webhook/send?key=" + notification.weComBotKey;
             let config = {
                 headers: {
                     "Content-Type": "application/json"
                 }
             };
             let body = this.composeMessage(heartbeatJSON, msg);
-            await axios.post(WeComUrl, body, config);
+            await axios.post(`https://qyapi.weixin.qq.com/cgi-bin/webhook/send?key=${notification.weComBotKey}`, body, config);
             return okMsg;
         } catch (error) {
             this.throwGeneralAxiosError(error);