TelemetryInitializers lack a DI friendly methods to add them

[RamjotSingh]

TelemetryProcessors(services.AddApplicationInsightsTelemetryProcessor) and TelemetryModules (services.ConfigureTelemetryModule) both have a DI friendly way of injecting them. TelemetryInitializers lacks any such method.

[RamjotSingh]

PR for reference which made TelemetryProcessors DI friendly.
#445

[cijothomas]

Injecting TelemetryInitializers is done via DI. (all ITelemetryInitializers injected to DI will become part of TelemetryConfiguration)
https://github.com/Microsoft/ApplicationInsights-aspnetcore/wiki/Custom-Configuration#adding-new-telemetryinitializer

Agree, we need something like ConfigureTelemetryInitializer.