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/serwersms.js

@@ -2,14 +2,14 @@ const NotificationProvider = require("./notification-provider");
 const axios = require("axios");
 
 class SerwerSMS extends NotificationProvider {
-
     name = "serwersms";
 
     /**
      * @inheritdoc
      */
     async send(notification, msg, monitorJSON = null, heartbeatJSON = null) {
-        let okMsg = "Sent Successfully.";
+        const okMsg = "Sent Successfully.";
+        const url = "https://api2.serwersms.pl/messages/send_sms";
 
         try {
             let config = {
@@ -25,7 +25,7 @@ class SerwerSMS extends NotificationProvider {
                 "sender": notification.serwersmsSenderName,
             };
 
-            let resp = await axios.post("https://api2.serwersms.pl/messages/send_sms", data, config);
+            let resp = await axios.post(url, data, config);
 
             if (!resp.data.success) {
                 if (resp.data.error) {