DDI improvements and Maintenance Window states in UI (#658)

* Add DDI status and tests.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Add new downloaded status to UI.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Reduce message noise.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Fix sonar issue.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

hawkbit-ddi-api/src/main/java/org/eclipse/hawkbit/ddi/json/model/DdiStatus.java

@@ -106,7 +106,12 @@ public class DdiStatus {
         /**
          * The action has been downloaded by the target.
          */
-        DOWNLOADED("downloaded");
+        DOWNLOADED("downloaded"),
+
+        /**
+         * Target starts to download.
+         */
+        DOWNLOAD("download");
 
         private String name;