Add span links capabilities to the OTel API

[PROFeNoM]

Description

Add the span links to the OpenTelemetry API.

Please note the following points about converting Datadog spans to OpenTelemetry (OTel) spans and creating span links:

• When converting a Datadog span to an OTel one, its current span links are also converted.
• When creating a span using the OTel API, the corresponding \DDTrace\SpanLink instances are also created.

It is important to note that span links can be added to a span at any point during its lifetime using the Datadog (DD) API, but such links can only be added using the OTel API during the build phase. This limitation is not a problem with the DD API but with the OTel API. To address this, DD span links are actualized onto the OTel span when creating an immutable span from it (toSpanData()). This is the only way to access the links associated with an OTel span. Span Links removal is supported and actualized during the same step.

Span Links limits aren't supported, as such a concept doesn't exist in the DD API and is irrelevant.

A WeakMap is used to store information about previously instantiated span links that are associated with an OpenTelemetry (OTel) span. When a span link is added to an OTel span, a one-to-one relationship is established between the SpanLink and Link instances to ensure consistency. This is necessary because duplicate span links are allowed. I'd advise to look at the added Interoperability Tests to understand better what I mean :)

Reviewer checklist

• Test coverage seems ok.
• Appropriate labels assigned.

[bwoebi]

Thanks! Looks good to me :-)

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-01-10 12:38:41

Comparing candidate commit in PR branch `` with baseline commit 77781a4 in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 36 metrics, 54 unstable metrics.