[#165] Fix scheduled migration via default cpp REP

Due to some changes in how scheduling data migrations works, the unified
storage tiering REP needed to be updated in order to work. The following
changes were made:

 - "policy" was changed to "policy_to_invoke" as expected in the cpp
default REP implementation of irods_policy_enqueue_rule
 - "payload" was changed to "parameters" as expected in the cpp default
REP implementation of irods_policy_enqueue_rule
 - "delay_conditions" was moved inside of the "parameters" JSON struct
as expected in the cpp default REP implementation of
irods_policy_enqueue_rule

This causes everything to align as expected in the new world of
policy-composed rule invocation.

storage_tiering.cpp

@@ -676,9 +676,8 @@ namespace irods {
 
         nlohmann::json rule_obj =
         {
-            {"policy", "irods_policy_enqueue_rule"}
-          , {"delay_conditions", _data_movement_params}
-          , {"payload",
+            {"policy_to_invoke", "irods_policy_enqueue_rule"}
+          , {"parameters",
                 {
                     {"rule-engine-operation",     policy::data_movement}
                   , {"rule-engine-instance-name", _plugin_instance_name}
@@ -690,6 +689,7 @@ namespace irods {
                   , {"destination-resource",      _destination_resource}
                   , {"preserve-replicas",         _preserve_replicas}
                   , {"verification-type",         _verification_type}
+                  , {"delay_conditions", _data_movement_params}
                 }
             }
          };