* ConfigOptions return an error, so we can react to things failing, rather than only reading it in the logs.
* Add unit tests.
* PR comments.
* PR comment - remove TODO.
* Expand the tracing package to support stackdriver.
This makes an assortment of changes to support the use of non-Zipkin tracing backends for publishing traces from system components based on config-tracing.
The changes to the config are modeled after config-observability, which already has support for prometheus and stackdriver backends for metrics.
* Incorporate review feedback.
* Incorporate feedback from @mdemirhan downstream
This moves around the code within the tracing package in preparation for adding support for other exporter options.
As the fields changed are all private, this should be a no-op for consumers of this package.
The goal of this change is to make it so that no files mention zipkin other than zipkin.go (or tests, which I left alone).
Adam Harwayne
Matt Moore
Akash Verenkar