Exporter: export Link from SpanData in Jaeger exporter

[rghetia]

Jaeger Exporter was added prior to Link support. Hence, Link is not exported via Jaeger exporter. See TODO

[paivagustavo]

Hi @rghetia!

I was playing with this issue but looks like the apitrace.Link structure does not have a "type of link" (seems like Jaeger accepts "child of" and "follows from") to map to Jaeger's SpanRefType.

So links are not getting exported even after uncomment the mentioned code. Hardcoding child_of works.

Should this be added to the api? Should we assume every link is a child_of relationship? Or is this not yet ready to be done?

[rghetia]

@paivagustavo for now hardcode child_of and add a TODO pending resolution of the issue open-telemetry/opentelemetry-specification#65.