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/clicksendsms.js

@@ -2,14 +2,15 @@ const NotificationProvider = require("./notification-provider");
 const axios = require("axios");
 
 class ClickSendSMS extends NotificationProvider {
-
     name = "clicksendsms";
 
     /**
      * @inheritdoc
      */
     async send(notification, msg, monitorJSON = null, heartbeatJSON = null) {
-        let okMsg = "Sent Successfully.";
+        const okMsg = "Sent Successfully.";
+        const url = "https://rest.clicksend.com/v3/sms/send";
+
         try {
             let config = {
                 headers: {
@@ -28,7 +29,7 @@ class ClickSendSMS extends NotificationProvider {
                     }
                 ]
             };
-            let resp = await axios.post("https://rest.clicksend.com/v3/sms/send", data, config);
+            let resp = await axios.post(url, data, config);
             if (resp.data.data.messages[0].status !== "SUCCESS") {
                 let error = "Something gone wrong. Api returned " + resp.data.data.messages[0].status + ".";
                 this.throwGeneralAxiosError(error);