feat(test-utils): add assertion helper for faas resources

[kaspernissen]

Which problem is this PR solving?

I'm currently trying to expand the resource detector for gcp and aligning it with the rest of the gcp resource detectors in other languages, that currently sets faas.name, faas.version, and faas.instance for Cloud Run services.

I have another PR open on this topic: #2818 where I will be using this helper.

Short description of the changes

This PR adds an assertion helper to the opentelemtry-test-utils package. Similarly to the rest of the assertion helpers it uses the semantic conventions and validates the inputs.

[pichlermarc]

Hi @kaspernissen - I would rather not have this be part of the @opentelemetry/contrib-test-utils unless it's commonly used across multiple packages. I think for now it would be better to have the assertion helper in @opentelemetry/resource-detector-gcp instead.

[kaspernissen]

Sure, I can do that for now. Reasoning behind putting it in the common, was to make it available for other packages.
I will close this PR and add it with the original PR 👍 Thanks for your swift reply!