refs https://github.com/TryGhost/Toolbox/issues/135
- Having the proxy in local utils allows to disable frontend gradually in test suites instead of all at once (the latter approach didn't work out as too many other suites still depend on full frontend initialization)
refs https://github.com/TryGhost/Team/issues/1217
- moved top-level `tenorApiKey` to `tenor:apiKey` and added `tenor:contentFilter`
- added base config to `defaults.json`
- updated `public-config.js` and API output serializer to use the new top-level `tenor` key
refs https://github.com/TryGhost/Team/issues/1217
- add `tenorApiKey` to `publicConfig.config()
- update canary config endpoint output serializer to include `tenorApiKey` when the `gifsCard` labs flag is enabled