x/build: add oauth2 to the dashboard #12775
Description
oauth2 package's continuous integration is outsourced to Travis for no good reason.
When we were bootstrapping the new oauth2 package, the Go project was migrating to the new build system and we opted for a quicker solution, Travis, while the x/build was still under work.
Since we have a stable CI system now, we can move the oauth2 package off of Travis.