The previous default sample rate of 0.0001 is very low, so traces are
unlikely to be visible after enabling them until many thousands of
requests have been sent. This could be confusing to users.
* metrics: support dynamic configuration settings
* add test
* trace: update configuration when settings change
* config: allow logging options to be configured when settings change
* envoy: allow changing log settings
* fix unexpected doc change
* fix tests
* pick a port at random
* update based on review
- Update envoy bootstrap config to protobufs
- Reorganize tracing config to avoid cyclic import
- Push down zipkin config to Envoy
- Update tracing options to provide sample rate
