Rehan/envoy subdomain

[RehanSD]

Must merge other PRs in. Put so progress can be seen

[simon-mo]

One more round to go. Great work!

[simon-mo]

Quick ping on this. And fixing the python package comments in closed PR

[simon-mo]

• use protobuf for categories
• json for models data and go code should just read it.
• use flags stdlib. (maybe cobra but too heavy weight)