Add new tail sampling processor policy: status_code

[yvrhdn]

Description:
This adds a new policy to the tail sampling processor sampling traces based upon the status code of a span. Adding this policy allows you to sample all traces of which the status code matches a given status code.

Link to tracking Issue:

Testing:

Added unit tests similar to the other policies.

⚠️ I haven't been able to write proper tests because I can't figure out how to set the status code on spans manually. All the pdata data structures are closed off: fields are private and there is not setter for status code 🤷🏻 If there is a mechanism to still set it, please let me know and I'll update the tests!

Documentation:

I have updated the README.

[yvrhdn]

We won't be able to merge this PR and #3750 at the same time because of merge conflicts, but I can resolve any conflicts in whatever PR we merge second.

[jpkrohling]

I haven't been able to write proper tests because I can't figure out how to set the status code on spans manually. All the pdata data structures are closed off: fields are private and there is not setter for status code

Doesn't this one here work?

https://github.com/open-telemetry/opentelemetry-collector/blob/0d747472e565e6548ebfe42a3b3205d29d9e9065/consumer/pdata/traces.go#L150-L162

[yvrhdn]

Doesn't this one here work?

https://github.com/open-telemetry/opentelemetry-collector/blob/0d747472e565e6548ebfe42a3b3205d29d9e9065/consumer/pdata/traces.go#L150-L162

🤯 yeah that works as you'd expect, not sure how I missed it 😅

[yvrhdn]

Rebased on top of #3787

[yvrhdn]

I'm going to pull this comment out of the review so it's easier to continue the discussion:

Don't we have status codes as attributes in the resource span attributes?

I'm not sure, I can't find anything that would say so. According to the spec the status is a separate field on a span (opentelemetry-specification/specification/trace/api.md#span).

I've been digging through the various resource attribtues, but haven't found anything related to the span status or status code. (opentelemetry-specification/specification/resource/semantic_conventions/README.md)

[yvrhdn]

(I'm going to rebase this again after #3787 and #3788 get merged, this will clean up the commits)

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 7 days.

[yvrhdn]

Friendly bump, this PR is still active I'm just waiting for a review 🙂

[mx-psi]

@kvrhdn can you fix the merge conflict?

@jpkrohling can you have another look?

[jpkrohling]

Looks good, the changelog needs to be changed though.

[jpkrohling]

I guess the latency made it to 0.29.0, no?

[jpkrohling]

Actually... 0.29.0 hasn't been released for contrib yet. I heard yesterday that the release train has departed already, though (#3863).

[yvrhdn]

Is it still possible to get this PR in 0.29 or is the release already cut?

[yvrhdn]

I'm not sure how to avoid a merge conflict with the release PR, should I wait until #3863 is merged to rebase and update the changelog?

[jpkrohling]

I think @bogdandrutu mentioned yesterday that they were having build problems, blocking the release. I don't expect any new features to be included for 0.29.0. Wait for the release, then rebase and update the changelog.