Promote process.env_vars to GA

[mjwolf]

Promote process.env_vars to GA. This field has been stabilized and in use for some time now, so it should be promoted to GA status.

• Have you signed the contributor license agreement?  ✅
• Have you followed the contributor guidelines? ✅
• For proposing substantial changes or additions to the schema, have you reviewed the RFC process? N/A
• If submitting code/script changes, have you verified all tests pass locally using make test? ✅
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• Is your pull request against main? Unless there is a good reason otherwise, we prefer pull requests against main and will backport as needed. ✅
• Have you added an entry to the CHANGELOG.next.md? ✅

[github-actions]

Documentation changes preview: https://ecs_2315.docs-preview.app.elstc.co/diff

[nick-alayil]

LGTM 👍