A pointer from the current Span to another span in the same trace or
in a different trace.
Few examples of Link usage.
Batch Processing: A batch of elements may contain elements associated
with one or more traces/spans. Since there can only be one parent
SpanContext, Link is used to keep reference to SpanContext of all
elements in the batch.
Public Endpoint: A SpanContext in incoming client request on a public
endpoint is untrusted from service provider perspective. In such case it
is advisable to start a new trace with appropriate sampling decision.
However, it is desirable to associate incoming SpanContext to new trace
initiated on service provider side so two traces (from Client and from
Service Provider) can be correlated.