[ReleasePR keyvault] Update description of trigger options (#1918)

Create to sync Azure/azure-rest-api-specs#16024
[ReCreate this PR](https://github.com/azure-resource-manager-schemas/compare/main...AzureSDKAutomation:sdkAuto/keyvault?expand=1)

Author: msftbot[bot]

schemas/2021-06-01-preview/Microsoft.KeyVault.json

@@ -1631,11 +1631,11 @@
       "properties": {
         "timeAfterCreate": {
           "type": "string",
-          "description": "The time duration after key creation to rotate the key. It should be in ISO8601 format. Eg: 'P90D', 'P1Y'."
+          "description": "The time duration after key creation to rotate the key. It only applies to rotate. It will be in ISO 8601 duration format. Eg: 'P90D', 'P1Y'."
         },
         "timeBeforeExpiry": {
           "type": "string",
-          "description": "The time duration before key expiring to rotate the key. It should be in ISO8601 format. Eg: 'P90D', 'P1Y'."
+          "description": "The time duration before key expiring to rotate or notify. It will be in ISO 8601 duration format. Eg: 'P90D', 'P1Y'."
         }
       }
     },