Kipartha/execution details action start end (Azure#18698)

* Add action start/end time.

* Update examples with action start/end times.

* fix typo in description.

Co-authored-by: kipartha <kipartha@microsoft.com>

Author: 2 people

specification/chaos/resource-manager/Microsoft.Chaos/preview/2021-09-15-preview/examples/GetAExperimentExecutionDetails.json

@@ -36,6 +36,8 @@
                         "name": "urn:provider:agent-v2:Microsoft.Azure.Chaos.Fault.CPUPressureAllProcessors",
                         "id": "59499d33-6751-4b6e-a1f6-58f4d56a040a",
                         "status": "failed",
+                        "startTime": "2020-12-14T13:56:13.6270153-08:00",
+                        "endTime": "2020-12-14T13:56:13.6270153-08:00",
                         "targets": [
                           {
                             "status": "succeeded",

specification/chaos/resource-manager/Microsoft.Chaos/preview/2021-09-15-preview/examples/ListExperimentExecutionsDetails.json

@@ -37,6 +37,8 @@
                             "name": "urn:provider:agent-v2:Microsoft.Azure.Chaos.Fault.CPUPressureAllProcessors",
                             "id": "59499d33-6751-4b6e-a1f6-58f4d56a040a",
                             "status": "failed",
+                            "startTime": "2020-12-14T13:56:13.6270153-08:00",
+                            "endTime": "2020-12-14T13:56:13.6270153-08:00",
                             "targets": [
                               {
                                 "status": "succeeded",
@@ -82,6 +84,8 @@
                             "name": "urn:provider:agent-v2:Microsoft.Azure.Chaos.Fault.CPUPressureAllProcessors",
                             "id": "59499d33-6751-4b6e-a1f6-58f4d56a040a",
                             "status": "success",
+                            "startTime": "2020-12-14T13:56:13.6270153-08:00",
+                            "endTime": "2020-12-14T13:56:13.6270153-08:00",
                             "targets": [
                               {
                                 "status": "succeeded",

specification/chaos/resource-manager/Microsoft.Chaos/preview/2021-09-15-preview/types/experiments.json

@@ -720,6 +720,18 @@
           "type": "string",
           "readOnly": true
         },
+        "startTime": {
+          "type": "string",
+          "format": "date-time",
+          "description": "String that represents the start time of the action.",
+          "readOnly": true
+        },
+        "endTime": {
+          "type": "string",
+          "format": "date-time",
+          "description": "String that represents the end time of the action.",
+          "readOnly": true
+        },
         "targets": {
           "description": "The array of targets.",
           "type": "array",