Publish code coverage reports to codecov

[breedx-splk]

This is a follow-up to #1211.

Much like the java core repo, it would be great to have our builds incorporate publishing coverage results to codecov. This is then used to display a summary report as an inline comment on each PR, and is also used to generate a build badge that we can display on the main page.

Having per-PR visibility help increase confidence that a given PR doesn't actually make things significantly worse test-wise. Furthermore, having a build badge on the main page (hopefully with good coverage!) can help new adopters gain confidence in the project's maturity.

[fractalwrench]

I'd be happy to help out with this one, although I'd need an assist from someone who has access to create this project in OpenTelemetry's codecov organisation. I think that alongside adding a GitHub secret to this repo are the two main things I don't have permission to do.

[breedx-splk]

I'd be happy to help out with this one, although I'd need an assist from someone who has access to create this project in OpenTelemetry's codecov organisation. I think that alongside adding a GitHub secret to this repo are the two main things I don't have permission to do.

Thanks for offering @fractalwrench. I have confirmation that the CODECOV_TOKEN is an org secret and can be used from an action, similar to how the java core repo does it.

Do we really need to pre-create a project in codecov, or maybe it's smart enough to know that an artifact upload/publish is for a new project?

[fractalwrench]

There does appear to be an existing project in codecov: https://app.codecov.io/github/open-telemetry/opentelemetry-android/new

I guess we'll see from the PR if any additional setup is required, but I think it should upload coverage once merged to main.