(PUP-3644) Move urls to v3

This removes the "v1" HTTP API, which mounted
all of the various Puppet endpoints at "/" on the webserver.

In its place we now have the "v3" API, which includes
the versioned "/v3" prefix for all of the indirected URLs.
The reason I moved this around was that based off the of the url structure we now have, for a request against e.g. `/v3/unknown`, it seemed more reasonable to throw a 404 and an error about not finding the indirection, rather than erroring over the environment (specified in the query param) not existing. Since checking for the environment's existence is done in `uri2indirection`, it was necessary to move this into `uri2indirection too, in order for it to happen first.