[DSM] Close span on produce error in ckgo

[mborst]

What does this PR do?

When the produce queue is full, the confluent-kafka-go producer returns a synchronous error. The span started in the wrapper for the produce call currently isn't Finished in this scenario.

Motivation

Stumbled upon during reading code.

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• Add an appropriate team label so this PR gets put in the right place for the release notes.
• Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.

For Datadog employees:

• If this PR touches code that handles credentials of any kind, such as Datadog API keys, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-02-16 10:55:29

Comparing candidate commit 444103c in PR branch mborst/fixes-for-dsm with baseline commit c86c219 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 41 metrics, 0 unstable metrics.

[sufianrhazi]

This makes sense to me, it seems like in case of an error we'd never close the span. Does this change also need to be performed in the kafka.v2 version?

dd-trace-go/contrib/confluentinc/confluent-kafka-go/kafka.v2/kafka.go

Lines 356 to 360 in 55ad19b

	err := p.Producer.Produce(msg, deliveryChan)
	// with no delivery channel, finish immediately
	if deliveryChan == nil {
	span.Finish(tracer.WithError(err))
	}

[mborst]

Good catch!