[WIP] Use OTLP exporter by default

[pellared]

Fixes #325

Changes proposed in this pull request:

• Use OTLP exporter by default.

Issues

1. On .NET Core for some reason the spans from the OTLP exporter do not reach the Collector. Possibly caused by bad configuration.

2. OTLP Exporter vs .NET Framework:

Unhandled Exception: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.TypeInitializationException: The type initializer for 'OpenTelemetry.ClrProfiler.Managed.Loader.Startup' threw an exception. ---> System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.IO.FileNotFoundException: Error loading native library. Not found in any of the possible locations: C:\Users\rpajak\repos\opentelemetry-dotnet-instrumentation\bin\tracer-home\net461\grpc_csharp_ext.x86.dll,C:\Users\rpajak\repos\opentelemetry-dotnet-instrumentation\bin\tracer-home\net461\runtimes/win/native\grpc_csharp_ext.x86.dll,C:\Users\rpajak\repos\opentelemetry-dotnet-instrumentation\bin\tracer-home\net461\../..\runtimes/win/native\grpc_csharp_ext.x86.dll
   at Grpc.Core.Internal.UnmanagedLibrary.FirstValidLibraryPath(String[] libraryPathAlternatives)
   at Grpc.Core.Internal.UnmanagedLibrary..ctor(String[] libraryPathAlternatives)
   at Grpc.Core.Internal.NativeExtension.LoadUnmanagedLibrary()
   at Grpc.Core.Internal.NativeExtension.LoadNativeMethods()
   at Grpc.Core.Internal.NativeExtension..ctor()
   at Grpc.Core.Internal.NativeExtension.Get()
   at Grpc.Core.GrpcEnvironment.GrpcNativeInit()
   at Grpc.Core.GrpcEnvironment..ctor()
   at Grpc.Core.GrpcEnvironment.AddRef()
   at Grpc.Core.Channel..ctor(String target, ChannelCredentials credentials, IEnumerable`1 options)
   at OpenTelemetry.Exporter.OtlpExporterOptionsExtensions.CreateChannel(OtlpExporterOptions options)
   at OpenTelemetry.Exporter.OpenTelemetryProtocol.Implementation.ExportClient.OtlpGrpcTraceExportClient..ctor(OtlpExporterOptions options, ITraceServiceClient traceServiceClient)
   at OpenTelemetry.Exporter.OtlpExporterOptionsExtensions.GetTraceExportClient(OtlpExporterOptions options)
   at OpenTelemetry.Trace.OtlpTraceExporterHelperExtensions.AddOtlpExporter(TracerProviderBuilder builder, OtlpExporterOptions exporterOptions, Action`1 configure, IServiceProvider serviceProvider)
   at OpenTelemetry.Trace.OtlpTraceExporterHelperExtensions.AddOtlpExporter(TracerProviderBuilder builder, Action`1 configure)
   at OpenTelemetry.ClrProfiler.Managed.Configuration.EnvironmentConfigurationHelper.SetExporter(TracerProviderBuilder builder, Settings settings) in C:\Users\rpajak\repos\opentelemetry-dotnet-instrumentation\src\OpenTelemetry.ClrProfiler.Managed\Configuration\EnvironmentConfigurationHelper.cs:line 87
   at OpenTelemetry.ClrProfiler.Managed.Configuration.EnvironmentConfigurationHelper.UseEnvironmentVariables(TracerProviderBuilder builder, Settings settings) in C:\Users\rpajak\repos\opentelemetry-dotnet-instrumentation\src\OpenTelemetry.ClrProfiler.Managed\Configuration\EnvironmentConfigurationHelper.cs:line 22
   at OpenTelemetry.ClrProfiler.Managed.Instrumentation.Initialize() in C:\Users\rpajak\repos\opentelemetry-dotnet-instrumentation\src\OpenTelemetry.ClrProfiler.Managed\Instrumentation.cs:line 78
   --- End of inner exception stack trace ---
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)      
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)       
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, 
CultureInfo culture)
   at OpenTelemetry.ClrProfiler.Managed.Loader.Startup.TryLoadManagedAssembly() in C:\Users\rpajak\repos\opentelemetry-dotnet-instrumentation\src\OpenTelemetry.ClrProfiler.Managed.Loader\Startup.cs:line 63
   at OpenTelemetry.ClrProfiler.Managed.Loader.Startup..cctor() in C:\Users\rpajak\repos\opentelemetry-dotnet-instrumentation\src\OpenTelemetry.ClrProfiler.Managed.Loader\Startup.cs:line 29
   --- End of inner exception stack trace ---
   at OpenTelemetry.ClrProfiler.Managed.Loader.Startup..ctor()
   --- End of inner exception stack trace ---
   at System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor, Boolean& bNeedSecurityCheck)
   at System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, StackCrawlMark& 
stackMark)
   at System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, StackCrawlMark& stackMark)
   at System.Activator.CreateInstance(Type type, Boolean nonPublic)
   at System.RuntimeType.CreateInstanceImpl(BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes, StackCrawlMark& stackMark)
   at System.Activator.CreateInstance(Type type, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes)
   at System.Reflection.Assembly.CreateInstance(String typeName, Boolean ignoreCase, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes)
   at __DDVoidMethodType__.__DDVoidMethodCall__()
   at GitCredentialManager.Program.Main(String[] args)

[RassK]

Maybe worth doing one per time. Eg let's start with .NET Core. Preprocessor directives could help in mean time setting the right default.

[nrcventura]

Maybe worth doing one per time. Eg let's start with .NET Core. Preprocessor directives could help in mean time setting the right default.

It's definitely worth splitting this up into 2 parts. Supporting .NET Standard 2.1+ apps (and .NET core 3.1+) apps should be an easier place to start because the OTLP exporter relies on a fully "managed" grpc implementation. Supporting the older frameworks will require figuring out how to package and load some of the native dependencies for the older and now deprecated grpc library.

Another alternative approach is to consider just supporting OTLP via protobufs over HTTP (instead of grpc).

[pellared]

Closing per #343