Fix process metrics registration when telemetry metrics level is none

[Arunodoy18]

Description

This PR fixes a regression introduced in v0.136.0 where custom compiled binaries for AIX (and other unsupported OSes) fail to start even when service.telemetry.metrics.level: none is configured.

Problem

Starting from v0.136.0, the OpenTelemetry Collector fails to start on platforms where gopsutil is not supported (such as AIX) with the following error:

Error: failed to register process metrics: not implemented yet

This occurs even when the service configuration explicitly sets:

service:
  telemetry:
    metrics:
      level: none
      
Solution
This change adds a conditional check before registering process metrics. The registration is now skipped when the telemetry metrics level is set to LevelNone, preventing errors on unsupported platforms.

The fix follows the same pattern used in other parts of the codebase (e.g., [metrics.go](vscode-file://vscode-app/c:/Users/aruno/AppData/Local/Programs/Microsoft%20VS%20Code/resources/app/out/vs/code/electron-browser/workbench/workbench.html)) where metrics functionality is disabled when level is set to none.

Changes
Added import for otelconftelemetry package to access telemetry configuration
Added conditional check to skip [RegisterProcessMetrics](vscode-file://vscode-app/c:/Users/aruno/AppData/Local/Programs/Microsoft%20VS%20Code/resources/app/out/vs/code/electron-browser/workbench/workbench.html) when [cfg.Telemetry.Metrics.Level == configtelemetry.LevelNone](vscode-file://vscode-app/c:/Users/aruno/AppData/Local/Programs/Microsoft%20VS%20Code/resources/app/out/vs/code/electron-browser/workbench/workbench.html)
Testing
This fix ensures that:

Collectors compiled for unsupported platforms (AIX, etc.) can start when metrics level is set to none
Process metrics are still registered on supported platforms when metrics level is not none
Related Issues
Fixes regression of #12098
Addresses the issue affecting all releases starting with v0.136.0

[Arunodoy18]

Thanks in advance for taking a look at this PR. I’ll actively follow up on feedback and make any required changes promptly—happy to adjust the approach or implementation as needed.

[dmitryax]

Please avoid unrelated changes

[dmitryax]

@Arunodoy18 do you have the PR that broke it?

Also, I'm not sure it's expected to require disabling the metrics on OSes unsupported by gopsutil. We don't document that. Maybe we just better ignore those particular metrics on the unsupported OSes?

[axw]

Also, I'm not sure it's expected to require disabling the metrics on OSes unsupported by gopsutil. We don't document that.

Agreed. It's also not what other instrumentation (e.g. otelhttp, as installed by confighttp) does.

Maybe we just better ignore those particular metrics on the unsupported OSes?

+1 and that's what #14319 does.

I suggest we close this.

[evan-bradley]

@Arunodoy18 Thank you for the PR! Based on the discussion here, and the reasoning given by @axw here #14319 (comment), I'm closing this PR in favor of #14319. I would encourage you to review that PR if you would like.

Sorry if this isn't an ideal outcome, sometimes things come out during PR discussion and we have to shift direction. We hope you'll contribute in the future!