Set cache patching default time as 5 hours (#18430)

Co-authored-by: Kanchan Joshi <[email protected]>

Author: koderjoker

specification/redis/resource-manager/Microsoft.Cache/stable/2020-12-01/redis.json

@@ -2397,7 +2397,8 @@
         "maintenanceWindow": {
           "type": "string",
           "format": "duration",
-          "description": "ISO8601 timespan specifying how much time cache patching can take. "
+          "description": "ISO8601 timespan specifying how much time cache patching can take.",
+          "default": "PT5H"
         }
       },
       "required": [