ConfigProvider#getInstrumentationConfig is inconsistent with the spec

[jack-berg]

With #7954 merged, ConfigProvider#getInstrumentationConfig is inconsistent with the spec.

We accepted this because as this comment mentioned, we're ok with this because its an incubating module.

However, we must reconcile the spec or the code before stabilizing.

[zeitlinger]

created open-telemetry/opentelemetry-specification#4817