State mach: fix: delete stale DbStatus after each wait

Fixes a subtle bug introduced by the use of the JSONata transition operator
with regular expression matches ( ~> |$|{'DbStatus': $match(...)} ) or with
queries that can fail. A failed match is very unlikely, and would signal a
change in the Aurora API. A failed query (of an RDS DescribeDBInstances result)
is unlikely but possible. So, it's important to handle this case correctly.
A failed match or failed query returns undefined, which leaves the key out of
the merge object. If DbStatus was set successfully on a previous iteration,
the old value persists. To prevent this, I now delete DbStatus, along with past
Error and Cause keys, at the end (Output) of the Wait state.

I chose not to do this in the Dispatch (former name) state, at the start of
an iteration, because that is a Choice state and it would be necessary to
duplicate the deletion code for DB_INSTANCE and CLUSTER.

Author: sqlxpert

step_stay_stopped_aws_rds_aurora.asl.json

@@ -145,8 +145,8 @@
     "Wait": {
       "Type": "Wait",
       "Seconds": "{% $Constant.StepFnWaitSeconds %}",
-      "Output": "{% $states.input ~> |$|{}, ['Error', 'Cause']| %}",
-      "Comment": "Deletes any past error",
+      "Output": "{% $states.input ~> |$|{}, ['DbStatus', 'Error', 'Cause']| %}",
+      "Comment": "Deletes possibly-stale status, and any past error",
       "Next": "IfEventNotExpiredChooseDbClusterOrInstance"
     },
     "Fail": {

step_stay_stopped_aws_rds_aurora.yaml

@@ -835,8 +835,8 @@ Resources:
             "Wait": {
               "Type": "Wait",
               "Seconds": "{% $Constant.StepFnWaitSeconds %}",
-              "Output": "{% $states.input ~> |$|{}, ['Error', 'Cause']| %}",
-              "Comment": "Deletes any past error",
+              "Output": "{% $states.input ~> |$|{}, ['DbStatus', 'Error', 'Cause']| %}",
+              "Comment": "Deletes possibly-stale status, and any past error",
               "Next": "IfEventNotExpiredChooseDbClusterOrInstance"
             },
             "Fail": {