refactored to make use of the ServiceType enum throughout backend and frontend for typesafety

backend/src/main/java/com/vaessl/app/connection/ConnectionRequest.java

@@ -3,9 +3,10 @@ package com.vaessl.app.connection;
 import com.fasterxml.jackson.annotation.JsonProperty;
 
 import jakarta.validation.constraints.NotBlank;
+import jakarta.validation.constraints.NotNull;
 
 public record ConnectionRequest(@NotBlank(message = "App URL is mandatory") String appUrl,
-                @NotBlank(message = "Service type is mandatory") String serviceType,
+                @NotNull(message = "Service type is mandatory") ServiceType serviceType,
                 String username, String password, String apiKey,
                 @JsonProperty(defaultValue = "false") Boolean stayLoggedIn) {
 
@@ -15,7 +16,7 @@ public record ConnectionRequest(@NotBlank(message = "App URL is mandatory") Stri
                 }
         }
 
-        public ConnectionRequest(String appUrl, String serviceType, String username,
+        public ConnectionRequest(String appUrl, ServiceType serviceType, String username,
                         String password, Boolean stayLoggedIn) {
                 this(appUrl, serviceType, username, password, null, stayLoggedIn);
         }