feat(faro/receiver): propagate request metadata to downstream consumers

[hainenber]

PR Description

Which issue(s) this PR fixes

Fixes #6503

Notes to the Reviewer

Added a E2E test for the whole flow but afraid that it's plagued with data race 😞 . Hope this can be circumvented by running the test without the race detector.

PR Checklist

• CHANGELOG.md updated
• Documentation added
• Tests updated

[clayton-cornell]

Doc change is small. Over to Agent team for code review.

[ptodev]

Thank you, and apologies for the late review! If it's hard to get the test working, maybe a simpler test will do for now?

[clayton-cornell]

This one is still sitting in my ToDos...
@hainenber there are some conflicts here that need to be resolved.
@ptodev is it ready for merge from your side once the conflicts are sorted?

[hainenber]

I've resolved the merge conflict. Re: simpler test for the change, most of metadata handling logic comes from internals of OpenTelemetry collectors so a E2E test is pretty much warranted. I think we can skip running data race for this particular test for the time being.

[rfratto]

@hainenber I'm really sorry about how long this (and your other PRs) have been sitting around; we've all been super busy preparing for GrafanaCon. Working on helping getting this merged now :)

[hainenber]

@rfratto no worries, the more GA users from GrafanaCon, the better for me also :D

Thanks for checking out my past PRs!