* Add tracing.HTTPSpanMiddlewareIgnoringPaths which will turn off tracing for the specified paths.
This is intended to allow us to ignore automated requests, such as liveness and readiness checks.
* PR comments.
* Rename HTTPSpanMiddlewareIgnoringPaths to HTTPSPanIgnoringPaths.
* 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).