Avoiding environment variable spec & doc drift

[chalin]

@cartermp, @austinlparker, @svrnm - Since

• Add common language-agnostic environment variable configuration docs #1432

we're now in a position where env. variables are described in two places, e.g.:

• https://opentelemetry.io/docs/reference/specification/sdk-environment-variables/#general-sdk-configuration
• https://opentelemetry.io/docs/concepts/sdk-configuration/general-sdk-configuration

Our effort from the start has been to try to keep things DRY, to avoid drift, etc. To resolve this we can:

• Remove the corresponding definitions from the spec (if they are considered non-normative)
• Generate the local docs directly from the spec.

Other suggestions?

Also related:

• Update OTLP SDK Config docs as per feedback #1441

[cartermp]

Hmm, in general I'm not opposed to trying to avoid drift, but I worry that it will lead to the wrong kind of content. There's a legitimate need to understand the spec, but the spec is at times not detailed enough (e.g, example usage) or far too detailed and clearly not written for a user of OpenTelemetry (e.g., explaining the exporter endpoint variables). I don't think we can change the spec here, but I really wouldn't want to make the spec just be the docs either.