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
• [x] Check whether OTEL tracker should also use the name build_info
• [x] Only call tracker set_build_info once

[brettimus]

Update: OTEL support will be dependent on resolution of https://github.com/open-telemetry/opentelemetry-python/issues/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

https://github.com/open-telemetry/opentelemetry-python/pull/3306