Update environment-variables.md

[mirnawong1]

this pr is a fast follow addressing @runleonarun 's feedback on repetitive content. so I've tried to make sure the content that applies to all is located clearly. and the content that applies to certain section clearly addresses the particular section

#5358 (comment)

What are you changing in this pull request and why?

Checklist

• Review the Content style guide so my content adheres to these guidelines.
• For docs versioning, review how to version a whole page and version a block of content.
• Add a checklist item for anything that needs to happen before this PR is merged, such as "needs technical review" or "change base branch."

Adding or removing pages (delete if not applicable):

• Add/remove page in website/sidebars.js
• Provide a unique filename for new pages
• Add an entry for deleted pages in website/vercel.json
• Run link testing locally with npm run build to update the links that point to deleted pages

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Comments	Updated (UTC)
docs-getdbt-com	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	May 1, 2024 9:19am