Add all environment variable values defined in the spec to the environment variables modules

[ocelotl]

We have environment variable modules for the API and SDK. There are some values defined in the corresponding spec section that are not included in these modules in an importable way (like default values).

This idea originates from this comment: https://github.com/open-telemetry/opentelemetry-python/pull/2968#discussion_r1002632332