Request tracking configuration improvements

[lmolkova]

In some cases, injection and auto-config via AddApplicationInsights is not convenient: not all features are needed or some very specific config needs to be done.

It's complicated for request collection:

1. RequestTrackingTelemetryModule configures HostingDiagnosticListener and MvcDiagnosticsListener.

Hosting is responsible for

• request tracking
• appId injection into the response

Mvc listener is responsible for exception tracking.

In some cases I want to configure only requests, but not exceptions or vice versa (e.g. for functions I want to configure requests only, but exceptions are tracked in a different way), so I suggest:

• configure them in a DI way: register list of IApplicationInsightDiagnosticListener in DI and pass the list as a parameter for RequestTrackingTelemetryModule
  OR
• split requests and exception tracking into 2 different modules.

2. OperationCorrelaitonTelemetryIntitializer extracts appId from the incoming request. It should be removed and done in hosting diagnostic listener.
   Also, the initializer is internal so configuring it in the app explicitly via DI is not possible

[lmolkova]

fixed in #716