This PR updates the tags that we generate for Envoy stats.
Several of these come with breaking changes, since we can't keep two stats prefixes for a filter.
* ui: Add functionality to metrics mocks:
1. More randomness during blocking queries
2. NaN and undefined values that come from prometheus
3. General trivial amends to bring things closer to the style of the
project
* Provider should always provide data as a string or undefined
* Use a placeholder `-` if the metrics endpoint responds with undefined data
* Add consul-api-double under api
* Update config to reflect api change
* Remove consul-api-double as a dependency
* api -> mock-api
* Fixup mocks path for staging
John Cowen