Make configuration of TelemetryChannel easy #641

TelemetryChannel is not configured via DI, hence it cannot be retrieved from DI by user.

Proposal is to add channel to DI just like other modules and initializers for consistency, if not already added by user.

The following line is all whats needed by user to control TelemetryChannel.
services.AddSingleton(typeof(ITelemetryChannel), new InMemoryChannel() {MaxTelemetryBufferCapacity = 19898 });