Support Correlation headers in the Django Middleware

[twschiller]

Add support for Correlation headers [1] in the Django Middleware.

Basic support would involve reading Request-Id in the header, and outputting as operation_Id in the telemetry.

[1] https://docs.microsoft.com/en-us/azure/application-insights/application-insights-correlation#correlation-headers

[jjjordanmsft]

The request ID is currently generated randomly; telemetry clients that get attached to the requests that are passed into the views have their parent operation ID set to the same. The missing piece is reading it in from the header.

[twschiller]

I was wrong. The request id should continue to be generated randomly. The operation_ParentId and operation_Id should be read from the Request-Id and Correlation-Context headers according to the flat/hierarchical request specification