Add build_info metric and use it in generated queries

[brettimus]

Implements #25

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Description for Reviewers

We should discuss how we want to pull in the commit and version info, especially in relation to the expected behavior in VSCode.

What Changed

• Add an instance method of set_build_info to both the Prometheus and Otel trackers

  • Make sure that set_build_info is only called once (per tracker instance)
  • Note that the OTEL tracker implements build_info as an UpDownCounter.

• When create_tracker is called, we will automatically call set_build_info with the AUTOMETRICS_COMMIT and AUTOMETRICS_VERSION environment variables

• Update PromQL queries to use commit and version info

TODO

• Update README regarding the environment variables we want to support for version/commit
• Check whether OTEL tracker should also use the name build_info
• Only call tracker set_build_info once

[brettimus]

Update: OTEL support will be dependent on resolution of open-telemetry/opentelemetry-python#3071 (I'm working on a PR)

[brettimus]

I think we can treat the OTEL support as non-blocking, since I'm not sure how long it will take for my PR on opentelemetry-python to get reviewed/merged/released

open-telemetry/opentelemetry-python#3306

[flenter]

🎉 Nice!

However, I think it would be good to expand the TrackerType protocol (i.e. interaface) with a set_build_info function (defined in src/autometrics/tracker/tracker.py)

[flenter]

The grafana dashboards use a slightly different query:

* on(instance, job) group_left(version, commit) (
    last_over_time(
      build_info[1s]
    ) or on (instance, job) up
  )

Perhaps we should do this here as well? Here's the PR with the related change on the autometrics-shared repo: autometrics-dev/autometrics-shared#8

[brettimus]

ah good catch! i updated the queries + tests

[flenter]

2 minor things, but in general LGTM! 👍