Real response from server end is not same with the swagger spec in application insight

ref https://github.com/Azure/azure-cli-extensions/issues/1221
In the swagger spec, customDimensions is defined as the following line.
https://github.com/Azure/azure-rest-api-specs/blob/master/specification/applicationinsights/data-plane/Microsoft.Insights/preview/v1/AppInsights.json#L1135
However, the real response is
```
"customDimensions": {
"ai_legacyRequestId": "XXXX",
"FunctionExecutionTimeMs": "2279.5392",
"TriggerReason": "This function was programmatically called via the host APIs.",
"FullName": "Functions.handler",
"LogLevel": "Information",
"Category": "Host.Results",
"InvocationId": "XXXX",
"HostInstanceId": "XXXX",
"ProcessId": "37",
"HttpMethod": "POST",
"HttpPath": "/api/handler"
},
```
This inconsistency cause problems in python SDK.