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-ddi/hawkbit-ddi-security/src/main/java/org/eclipse/hawkbit/security/controller/Authenticator.java

@@ -11,6 +11,7 @@ package org.eclipse.hawkbit.security.controller;
 
 import static org.eclipse.hawkbit.context.AccessContext.asTenant;
 
+import java.io.Serial;
 import java.util.Collection;
 import java.util.List;
 import java.util.Objects;
@@ -61,6 +62,9 @@ public interface Authenticator {
         @EqualsAndHashCode(callSuper = true)
         private static class AuthenticatedController extends AbstractAuthenticationToken {
 
+            @Serial
+            private static final long serialVersionUID = 1L;
+
             private static final Collection<GrantedAuthority> CONTROLLER_AUTHORITY =
                     List.of(new SimpleGrantedAuthority(SpRole.CONTROLLER_ROLE));
             private final String controllerId;