SDK env var config Enum values are case-insensitive

[pellared]

What

Enum values provided via environment variables SHOULD be interpreted in a case-insensitive manner.
When reporting configuration errors, implementations SHOULD display the original user-provided value to aid debugging.

Why

This improves user experience by allowing more flexible configuration (e.g., OTEL_EXPORTER_OTLP_PROTOCOL=grpc and OTEL_EXPORTER_OTLP_PROTOCOL=gRPC can be treated equivalently).

This improves consistency as it is also similar to the Boolean definition which has many in common to Enum type:

Any value that represents a Boolean MUST be set to true only by the case-insensitive string "true"

Implementations

Here is an example from OTel Go (existing code from main branch) where OTEL_TRACES_SAMPLER enum value is lower-cased before comparing with known-values:

https://github.com/open-telemetry/opentelemetry-go/blob/118298edcfd5a38c7eb767bc290a528d380a79fd/sdk/trace/sampler_env.go#L49-L54

[tsloughter]

Oops, only way to undo an approval is to make a comment it seems.

Dismissing 😉

[pellared]

Oops, only way to undo an approval is to make a comment it seems.

Not really. I dismissed your approval.

[carlosalberto]

Let's advertise this PR in the next spec call so maintainers can double check it.