Add Instrumentation

[samritchie]

metricsCollector was added to TableContext approx three years ago as a stop-gap for plugging observability features into Dynamo. Since then the dotnet observability story has solidified around OpenTelemetry exposed via Systems.Diagnostics counters/activities.

There is beta AWS SDK instrumentation available in OpenTelemetry.Instrumentation.AWS, however this appears to be fairly limited to the outer API calls rather than anything dynamo-specific.

I’m suggesting deprecating the metricsCollector param and adding System.Diagnostics instrumentation to this library directly. There are recommended attributes published at https://opentelemetry.io/docs/specs/semconv/database/dynamodb/. A few questions for discussion:

• Should this include logging, metrics, traces or all three? I don’t think anyone’s missed library-level logging so far, but it may end up being useful for streams
• Should the recommended attributes be implemented verbatim or should it just implement the essentials to start with
• Conventionally libraries publish a separate package with a (very basic) hosting extension to enable metrics/traces on the application host. I’m unsure whether this is really necessary, or even how many consuming applications use Host builders