feat(gcp-detector): add Cloud Run support with faas.* and cloud.platform

[kaspernissen]

Which problem is this PR solving?

The resource detector for gcp did not previously support Cloud Run–specific resource attributes, although these are supported in other SDKs (e.g. Go, Java). This PR adds support for setting the faas.* along with cloud.platform resource attributes when running in a Cloud Run environment.

Short description of the changes

• Detects faas.name from K_SERVICE environment variable.
• Detects faas.version from K_REVISION environment variable
• Detects faas.instance from GCP metadata server (/instance/id) reusing the existing method.
• Sets cloud.platform using the semantic conventions static variables.
• Adds unit test for Cloud Run detection, following existing patterns
• Keeps full backward compatibility and aligns behavior with the Go SDK implementation (using env vars)

For more information, see the container runtime contract: https://cloud.google.com/run/docs/container-contract#env-vars.

This is my first PR 🙏

I've added another PR for the extension of the assertCloudResource helper with cloud.platform. For now just manually asserting in the test case.

[mmanciop]

I am looking forward to seeing this merged :-)

[pichlermarc]

cc @punya and @aabmass (component owners)

[punya]

I am no longer working in this area, @aabmass could you please take a look, and also update component owners?

[david-luna]

@aabmass could you have a look at this one? I could volunteer to review it but I think you feedback would be better

[aabmass]

Hey, apologies for the confusion. We have already implemented this in @google-cloud/opentelemetry-resource-util detector.

I would actually like to make the resource detector here in contrib just re-expose the one from @google-cloud/opentelemetry-resource-util: GoogleCloudPlatform/opentelemetry-operations-js#518

I previously discussed this with the maintainers and it wasn't contentious but haven't found the time to do it. To recap, the reason to use it as a library vs copying the code is that we have a bunch of integration tests that would be really difficult to move to this repo.