Fix some compile warnings (#2919)

* Fix some compile warnings
* Some classes made final
* JPA entities made not serializable

Signed-off-by: Avgustin Marinov <Avgustin.Marinov@bosch.com>

hawkbit-mcp/pom.xml

@@ -61,12 +61,6 @@
             <artifactId>spring-ai-mcp-annotations</artifactId>
         </dependency>
 
-        <dependency>
-            <groupId>org.springframework.boot</groupId>
-            <artifactId>spring-boot-configuration-processor</artifactId>
-            <optional>true</optional>
-        </dependency>
-
         <dependency>
             <groupId>com.github.ben-manes.caffeine</groupId>
             <artifactId>caffeine</artifactId>