RFC: Experimental profiling

[dmathieu]

Description

This is an RFC discussing the proposed solution for adding the profiling signal.
Follows #10207

PoC: #10307

cc @open-telemetry/profiling-triagers @open-telemetry/profiling-approvers @open-telemetry/profiling-maintainers
cc @open-telemetry/collector-approvers

[christos68k]

LGTM

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.36%. Comparing base (ea7270c) to head (ae8072d).

Additional details and impacted files

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##             main   #10375   +/-   ##
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  Coverage   92.36%   92.36%           
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  Files         386      386           
  Lines       18400    18400           
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  Hits        16995    16995           
  Misses       1052     1052           
  Partials      353      353           

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[codeboten]

Thanks @dmathieu, this looks great. Just one comment

[mx-psi]

@dmathieu I think #10253 is a possible way to address this, since it addresses this:

But this can't work, as the WithProfiles method needs to manipulate private values, and can't do that from an outside module.

Could you take a look and let me know if that addresses the issue?

[mx-psi]

I think we can merge this as is and as noted on the Collector SIG I believe we can merge this on Friday.

One remaining step is what to do with service and <receiver|exporter|connector|processor>.Builder. The problem is that we don't pass the configuration directly to the service and instead pass Builders. These builders encapsulate the factories and config, thus we lose access to the config.

We will need to solve this problem during implementation, some options are:

1. Add a Config method to builders similar to the Factory method
2. Make builders internal to the service and pass the config and factories explicitly (honestly at this point my preferred option, there is no real abstraction/usefulness to have these exposed)
3. Make the builders into sealed interfaces like with the factory interfaces? (not sure if there's much of a point for this)

[dmathieu]

Following a discussion with @mx-psi this morning, we have decided to follow option 2 mentioned above for the builders.

[atoulme]

I have pasted this in a couple PRs, pasting it here as well:

Before we break the API, we typically deprecate it for at least one release. More here: https://github.com/open-telemetry/opentelemetry-collector/blob/main/CONTRIBUTING.md#breaking-changes

[dmathieu]

Sure, I've done that in all 5 PRs.