[Bug]: Lambda detector returns error if not run in Lambda

[milas]

Component

Detector: AWS Lambda

Describe the issue you're facing

The detector does not fail gracefully if not run in Lambda, so can't be used generically.

This is inconsistent with, e.g. the EKS detector that no-ops once it determines it's not in-cluster, returns gracefully

Expected behavior

No error returned when detector is not used in Lambda env:

	// Lambda resources come from ENV
	lambdaName := os.Getenv(lambdaFunctionNameEnvVar)
	if lambdaName == "" {
		return empty, errNotOnLambda
	}

⬇️

	// Lambda resources come from ENV
	lambdaName := os.Getenv(lambdaFunctionNameEnvVar)
	if lambdaName == "" {
		return empty, nil
	}

Steps to Reproduce

	res, err := resource.New(
		ctx,
		resource.WithDetectors(
			lambdadetector.NewResourceDetector(),
		),
	)

And launch locally.

Operating System

Linux (distroless/container)

Device Architecture

ARM64

Go Version

1.25.7

Component Version

v0.66.0

[milas]

I am happy to submit a Pull Request for this if the behavior I've described is desirable.

This also might be worth doing before stabilizing as v1 (see #8423).

[dmathieu]

cc @akats7 as code owner.

[dmathieu]

This change makes sense to me.

[pellared]

I also think that this change makes sense.
@milas, feel free to submit a PR.