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/telegram.js

@@ -2,14 +2,14 @@ const NotificationProvider = require("./notification-provider");
 const axios = require("axios");
 
 class Telegram extends NotificationProvider {
-
     name = "telegram";
 
     /**
      * @inheritdoc
      */
     async send(notification, msg, monitorJSON = null, heartbeatJSON = null) {
-        let okMsg = "Sent Successfully.";
+        const okMsg = "Sent Successfully.";
+        const url = "https://api.telegram.org";
 
         try {
             let params = {
@@ -22,7 +22,7 @@ class Telegram extends NotificationProvider {
                 params.message_thread_id = notification.telegramMessageThreadID;
             }
 
-            await axios.get(`https://api.telegram.org/bot${notification.telegramBotToken}/sendMessage`, {
+            await axios.get(`${url}/bot${notification.telegramBotToken}/sendMessage`, {
                 params: params,
             });
             return okMsg;