Mark Versioning documents as stable (#1409)
Mark Versioning documents as stable (#1409)

* mark versioning as stable

* mark sdk env vars as stable

* Update sdk-environment-variables.md

Co-authored-by: Bogdan Drutu <1078cf414b2625a240b16392085d66580bb66f4d@splunk.com>
Co-authored-by: Bogdan Drutu <3f8e17047c2434e5c82a61403e56b9ef3e226d99@gmail.com>
open-telemetry/opentelemetry-specification,open-telemetry/opentelemetry-specification