Add support for detecting MIG attributes on GCE VMs

[quentinmit]

This adds support for two new resource attributes, gcp.gce.instance_group_manager.name and gcp.gce.instance_group_manager.{zone,region}, that indicate the managed instance group that a Compute Engine VM is part of. The equivalent Collector change is in open-telemetry/opentelemetry-collector-contrib#36142

[codecov]

Codecov Report

Attention: Patch coverage is 78.57143% with 3 lines in your changes missing coverage. Please review.

Project coverage is 68.5%. Comparing base (00786cc) to head (e755523).
Report is 23 commits behind head on main.

Files with missing lines	Patch %	Lines
detectors/gcp/detector.go	78.5%	3 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #6538   +/-   ##
=====================================
  Coverage   68.5%   68.5%           
=====================================
  Files        200     200           
  Lines      16768   16782   +14     
=====================================
+ Hits       11490   11501   +11     
- Misses      4933    4936    +3     
  Partials     345     345           

Files with missing lines	Coverage Δ
detectors/gcp/detector.go	83.1% <78.5%> (-0.7%)	⬇️

[MrAlias]

Please address the lint failures.

[MrAlias]

Please open an issue to track the work needed to resolve these TODOs and reference the issue in this comment.

[MrAlias]

Missing test for this error.

[MrAlias]

Indentation can be reduced by restructuring:

Suggested change

	if mig, err := detect(); err == nil {
	if mig.Name != "" {
	r.attrs = append(r.attrs, gcpGceInstanceGroupManagerNameKey.String(mig.Name))
	}
	switch mig.Type {
	case gcp.Zone:
	r.attrs = append(r.attrs, gcpGceInstanceGroupManagerZoneKey.String(mig.Location))
	case gcp.Region:
	r.attrs = append(r.attrs, gcpGceInstanceGroupManagerRegionKey.String(mig.Location))
	}
	} else {
	r.errs = append(r.errs, err)
	}
	mig, err := detect()
	if err != nil {
	r.errs = append(r.errs, err)
	return
	}
	if mig.Name != "" {
	r.attrs = append(r.attrs, gcpGceInstanceGroupManagerNameKey.String(mig.Name))
	}
	switch mig.Type {
	case gcp.Zone:
	r.attrs = append(r.attrs, gcpGceInstanceGroupManagerZoneKey.String(mig.Location))
	case gcp.Region:
	r.attrs = append(r.attrs, gcpGceInstanceGroupManagerRegionKey.String(mig.Location))
	}