[processor/transform] Add debug log that prints current TransformContext

[TylerHelmuth]

Component(s)

processor/transform

Is your feature request related to a problem? Please describe.

We see a lot of transformprocessor questions that boil down to the data being manipulated looking slightly different in the collector than it does in backends, leading to incorrect OTTL statements. What we do now is ask users to add debugexporters to their pipelines and view the output. This works, but is extra steps.

Describe the solution you'd like

It would be nice if, when the service.telemetry.logs.level=debug, the transformprocessor printed out a log that contained the details of the current TransformContext. This is essentially the some result as using the debugexporter, but doesn't require configuring any extra components and is much more targeted to just the transformprocessor's data.

I experiment with this idea briefly and it isn't difficult to get a logger to the right place in the transformprocessor. The hard part is getting the underlying pdata structs to print nicely. I believe each TransformContext type will need a String() string{} that returns the string representation of the TransformContext.

Describe alternatives you've considered

No response

Additional context

No response

[github-actions]

Pinging code owners for processor/transform: @TylerHelmuth @kentquirk @bogdandrutu @evan-bradley. See Adding Labels via Comments if you do not have permissions to add labels yourself.

[TylerHelmuth]

@dmitryax are there any existing patterns for converting a ptrace.span to a string? I see https://github.com/open-telemetry/opentelemetry-collector/tree/main/exporter/internal/otlptext but it appears to work only on the top-level data slices for all 3 signals.

[TylerHelmuth]

Duplicate of #30932