fix: Only add Redis instrumentation if connection found in DI

[MikeGoldsmith]

Which problem is this PR solving?

Apps that do not utilise Redis and register a connection before calling AddAutoInstrumentations fail to send telemetry. This is because even though the AddRedisInstrumentation call has the connection as an optional parameter, an exception is thrown if a connection is not provided and one cannot be found in DI.

This PR updates AddAutoInstrumentations to try to find a Redis connection from DI and only call AddRedisInstrumentation if one is found.

• Closes AddAutoInstrumentations fails due to missing config for AddRedisInstrumentation #322

Short description of the changes

• Only add Redis instrumentation if a registered Redis connection is found using DI

[JamieDanielson]

Hmm, I'm still having trouble even after this change.

I used the aspnetcore example app, and on its own with .AddAspNetCoreInstrumentationWithBaggage() it sends a trace with 2 spans. When I swap that out with .AddAutoInstrumentations(), it does not send any traces.

I enabled diagnostics by setting up a file for OTEL_DIAGNOSTICS.json. In the error log I see the following:

2022-11-21T15:45:01.0061910Z:An exception occurred while retrieving OpenTelemetry Tracer. OpenTelemetry tracing will remain disabled. Exception: '{0}'.{System.InvalidOperationException: StackExchange.Redis IConnectionMultiplexer could not be resolved through application IServiceProvider
   at OpenTelemetry.Trace.TracerProviderBuilderExtensions.<>c__DisplayClass0_0.<AddRedisInstrumentation>b__0(IServiceProvider sp, TracerProviderBuilder builder)

...

[MikeGoldsmith]

I followed the same steps as you @JamieDanielson and my app continued to send telemetry - not sure what else was different

[JamieDanielson]

Ah! Looks like I may have been using the Nuget-published package instead of the local project reference 🙈

I updated my aspnetcore.csproj to have <ProjectReference Include="..\..\src\Honeycomb.OpenTelemetry.AutoInstrumentations\Honeycomb.OpenTelemetry.AutoInstrumentations.csproj" /> instead of <PackageReference Include="Honeycomb.OpenTelemetry.AutoInstrumentations" Version="0.26.0-beta" /> and indeed, I have a trace with 2 spans!

Looks good!