SDK: Determine how to convert OpenTelemetry::Resources into Jaeger

[jpkrohling]

During the review for #481, the topic about converting OpenTelemetry Resources into Jaeger came up. Once it's clear what's to be done, the Adapter's toJaeger method needs to incorporate this conversion.

Context:
#481 (comment)

[pavolloffay]

The resource is set on only on tracer at the moment. We can treat it as process information which maps to Process struct in Jager. We could get the resource from the first span and merge it with the process created at exporter startup. We do the same in Jaeger client exporters.

[songy23]

FYI in opentelemetry-service we translate resource into Jaeger process tags: open-telemetry/opentelemetry-collector#325.

[thisthat]

open-telemetry/opentelemetry-specification#848 has been resolved. Resources must be mapped to process tags: spec link.

[jkwatson]

We should probably change the title of this issue to match the fact that it just needs to be implemented now. :)

[jkwatson]

Aha. This is now a dupe of #1609 . I'll revert the title change for this issue and close it, now that the spec is done.

[jkwatson]

Closing, now that the spec is complete and #1609 is ready to be implemented.