Go server support

[dmueller]

Problem

We're getting a Go service up and running and want to be able to get some business metrics that will help inform our decisions and awareness of how the ads funnel is performing. Some of these metrics will correlate with client telemetry, so we want to be able to collect them and analyze them in BQ for convenience (to avoid having to compare data from service monitoring dashboard and then have difficulty correlating them, or worry about having different retention durations between data in different systems)

Solution

Following the patterns of ruby_server and js_server, this adds support for go_server. It only supports the "events" ping and doesn't support custom pings -- this is a difference between ruby_server and js_server, but it was an intentional decision to leave it out from ruby_server and we want that to be the pattern going forward for server implementations.

The go_server implementation supports all three currently allowed types in the extra_keys field for event metrics, and supports string and quantity metrics as well. We expect numeric data to be common (e.g. how many ads were returned to the client), so that is another difference between go_server and the other two existing ones.

The generated code hasn't yet been deployed in GCP to confirm the flow in its entirety, so there may be some follow up adjustments with that step.

Pull Request checklist

• Quality: This PR builds and tests run cleanly
  • make test runs without emitting any warnings
  • make lint runs without emitting any errors
• Tests: This PR includes thorough tests or an explanation of why it does not
• Changelog: This PR includes a changelog entry to CHANGELOG.md or an explanation of why it does not need one
  • Any breaking changes to language binding APIs are noted explicitly

[akkomar]

r+wc

LGTM, I have successfully tested this end to end in a staging project.

[badboy]

one thing blocking this, once fixed this should be good to go.

[badboy]

thank you