[ReleasePR redis] Set cache patching default time as 5 hours (#2143)

Create to sync Azure/azure-rest-api-specs#18430
[ReCreate this PR](https://github.com/azure-resource-manager-schemas/compare/main...AzureSDKAutomation:sdkAuto/redis?expand=1)

Author: msftbot[bot]

schemas/2020-12-01/Microsoft.Cache.json

@@ -817,8 +817,9 @@
         },
         "maintenanceWindow": {
           "type": "string",
+          "default": "PT5H",
           "format": "duration",
-          "description": "ISO8601 timespan specifying how much time cache patching can take. "
+          "description": "ISO8601 timespan specifying how much time cache patching can take."
         },
         "startHourUtc": {
           "oneOf": [