implemented basic search function with Homebox provider

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

@@ -0,0 +1,10 @@
+package com.vaessl.app.connection;
+
+public interface ServiceProvider {
+
+    /**
+     * Returns the service type key used to look up this provider in a registry, e.g.
+     * {@code "HOMEBOX"}.
+     */
+    String getServiceType();
+}