Updating the EventHubNameParameter max length to 256 (#10401)

Co-authored-by: Mytri Ramanathpur Manjunath (MINDTREE LIMITED) <[email protected]>

Author: Ajit Navasare

specification/eventhub/resource-manager/Microsoft.EventHub/common/v1/definitions.json

@@ -126,7 +126,7 @@
       "required": true,
       "type": "string",
       "minLength": 1,
-      "maxLength": 50,
+      "maxLength": 256,
       "x-ms-parameter-location": "method",
       "description": "The Event Hub name"
     },