extend go_server outputter to support custom pings

[dmueller]

Problem

https://mozilla-hub.atlassian.net/browse/AE-576

For our server integration in go we would like to use custom pings, as this will give more flexibility into how the data gets organized in BQ when we have more than one ping.

Solution

Adjust error message scenarios in go_server so that it is OK for pings to be defined, and OK if the events ping is not used. The go_server outputter now suppports only events ping, only custom ping(s), or both.

Added more test yaml configuration for each of these three scenarios, since they emit different methods in the templated code.

Enabled boolean support, since the code was already present to support booleans-as-strings in event extra; so now we will also support boolean metric values as well.

Added "time" to test.go.tmpl so that in the unit tests we can populate the datetime field with a value instead of leaving it with a default.

Testing

make test-full

I haven't run this in a place that would actually ingest the logged output, but have run the code similar to how the unit test runs test.go to see a log statement printed to stdout. This would be helpful to confirm that the statement is formatted as expected.

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
  • make test-full runs without any test failures
• 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]

Regarding the template: instead of treating events ping as special case, can we generalize the current approach to custom pings?
This would reduce code duplication and make Go template consistent with others (https://github.com/mozilla/glean_parser/blob/main/glean_parser/templates/javascript_server.jinja2, https://github.com/mozilla/glean_parser/blob/main/glean_parser/templates/python_server.jinja2)

[akkomar]

LGTM, my only suggestions are about docs and comments to make them (hopefully) clearer.

I haven't run this in a place that would actually ingest the logged output, but have run the code similar to how the unit test runs test.go to see a log statement printed to stdout. This would be helpful to confirm that the statement is formatted as expected.

Last two tests in test_go_server.py validate output against Glean schema. I have also tested this manually with ingestion Decoder and haven't seen any issues.