Make exposed CORS headers configurable (#1322)

* Prevent losing headers (like CORS related ones) when resetting the response headers due to artifact stream.

* add comment

* Extend CORS tests to verify provided header.

hawkbit-autoconfigure/src/main/java/org/eclipse/hawkbit/autoconfigure/security/SecurityManagedConfiguration.java

@@ -591,6 +591,7 @@ public class SecurityManagedConfiguration {
             corsConfiguration.setAllowCredentials(true);
             corsConfiguration.setAllowedHeaders(securityProperties.getCors().getAllowedHeaders());
             corsConfiguration.setAllowedMethods(securityProperties.getCors().getAllowedMethods());
+            corsConfiguration.setExposedHeaders(securityProperties.getCors().getExposedHeaders());
 
             return corsConfiguration;
         }