feat(detectors/gcp): add parity for BMS, Cloud Run Worker Pool, GCE MIG, and GKE hostname

[dashpole]

Part of #8946

Description

Brings feature parity to detectors/gcp to match the detector capabilities present in opentelemetry-collector-contrib's resourcedetectionprocessor:

1. Bare Metal Solution (BMS): Check for Bare Metal Solution before the GCE metadata check, and emit BMS resource attributes (cloud.platform = "gcp_bare_metal_solution", cloud.account.id, host.name, cloud.region).
2. Cloud Run Worker Pool: Handle CloudRunWorkerPool identically to CloudRun.
3. GCE Managed Instance Group (MIG): Detect MIG attributes (gcp.gce.instance_group_manager.name, zone, region) on GCE.
4. Best-effort GKE Hostname: Attempt to collect host.name on GKE nodes when available.

This is required for the collector to migrate to using this detector: open-telemetry/opentelemetry-collector-contrib#50211.

[Copilot]

Pull request overview

This PR extends detectors/gcp to match additional environment/resource-detection capabilities found in the Collector’s GCP resource detection, adding support for Bare Metal Solution (BMS) and Cloud Run Worker Pool parity, plus extra metadata on GCE and GKE.

Changes:

• Add Bare Metal Solution (BMS) detection and emit BMS-specific resource attributes.
• Treat CloudRunWorkerPool the same as CloudRun, and add best-effort host.name enrichment for GKE nodes.
• Detect and emit GCE Managed Instance Group (MIG) attributes on GCE.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
detectors/gcp/types.go	Extends the internal detector interface with MIG and BMS detection methods.
detectors/gcp/README.md	Documents BMS as a supported detection environment.
detectors/gcp/detector.go	Implements BMS short-circuit detection, Cloud Run Worker Pool handling, MIG attribute emission, and best-effort GKE hostname enrichment.
detectors/gcp/detector_test.go	Adds/extends unit tests covering MIG, Cloud Run Worker Pool, BMS, and GKE hostname behavior.

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[codecov]

Codecov Report

❌ Patch coverage is 92.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.5%. Comparing base (b876894) to head (147f2d6).

Files with missing lines	Patch %	Lines
detectors/gcp/detector.go	92.0%	2 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #9462   +/-   ##
=====================================
  Coverage   84.5%   84.5%           
=====================================
  Files        203     203           
  Lines      16805   16828   +23     
=====================================
+ Hits       14204   14225   +21     
- Misses      2121    2123    +2     
  Partials     480     480           

Files with missing lines	Coverage Δ
detectors/gcp/detector.go	88.0% <92.0%> (+0.8%)	⬆️

... and 2 files with indirect coverage changes

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[ps-mir]

@dashpole Does the scope also includes changes required for detector migration ?

#8946

If so, you can take the ownership of the task as well.

[dashpole]

Ah, I forgot that issue existed. Sorry for taking it without asking.

[dashpole]

I just need to add gcp.gce.instance.labels.* support, and move the library from opentelemetry-operations-go here.

[ps-mir]

Ah, I forgot that issue existed. Sorry for taking it without asking.

No issues :)

[dashpole]

I just need to add gcp.gce.instance.labels.* support, and move the library from opentelemetry-operations-go here.

I'll do those as follow-ups

[ps-mir]

Comments on error handling and semconv helpers in tests.

[ps-mir]

Small concern on CloudPlatform() being called twice for detection.

[ps-mir]

LGTM