Add support for dynamic rollout group template (#1752)

1. Add support in REST and Mgmt API for dynamic group template
2. If present - groups follows the pattern of this template, otherwise - the last static group
3. This allows to create pure dynamic rollout with 0 static groups - auto assignment equivalent with groups

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

hawkbit-repository/hawkbit-repository-core/src/main/java/org/eclipse/hawkbit/repository/RolloutHelper.java

@@ -78,7 +78,7 @@ public final class RolloutHelper {
      */
     public static void verifyRolloutGroupParameter(final int amountGroup, final QuotaManagement quotaManagement) {
         if (amountGroup <= 0) {
-            throw new ValidationException("The amount of groups cannot be lower than zero");
+            throw new ValidationException("The amount of groups cannot be lower than or equal to zero for static rollouts");
         } else if (amountGroup > quotaManagement.getMaxRolloutGroupsPerRollout()) {
             throw new AssignmentQuotaExceededException(
                     "The amount of groups cannot be greater than " + quotaManagement.getMaxRolloutGroupsPerRollout());