Migrate PMT to the /v3 API

Prior to this commit, the PMT managed all communication with the Forge via the
(now legacy) /v1 API. That API has been deprecated (primarily due to scalability
concerns), which is less of an issue since it was never officially a public API.

This commit migrates all communication to the Forge to the new /v3 API, which is
expected to be launched as our official public API "soon".