refactor: final migration of API to go

[michaelkedar]

• Update build-and-stage to build the new go API image
• Update Cloud Run configs to set new environment variables for the go API'
• Updated integration tests to run against go API
  • I might translate these wholly to go later, but it's a bigger project
• Updated Makefile targets to do go API instead
• Added some missing checks/features to the go API