Update configuring-astro.md

[natemoo-re]

What kind of changes does this PR include?

• [ ] Minor content fixes (broken links, typos, etc.)
• [x] New or updated content
• [ ] Translated content
• [ ] Changes to the docs site code
• [ ] Something else!

Description

• Adds a new section to configuring-astro.md about referencing environment variables.
• Also mentions Astro's ability to load config files from the config/ directory, a hidden feature that I personally love and hope more people start using!
• Paired with https://github.com/withastro/astro/pull/3617

[netlify[bot]]

✅ Deploy Preview for astro-docs-2 ready!

Name	Link
🔨 Latest commit	d788ffe27d608969b6ef3f2d1057124d5d25a7eb
🔍 Latest deploy log	https://app.netlify.com/sites/astro-docs-2/deploys/62abb27d74ad140008c3ae39
😎 Deploy Preview	https://deploy-preview-785--astro-docs-2.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.

[sarah11918]

LGTM! 🥳

[sarah11918]

Just a freshness ping, @natemoo-re ! You might not be used to looking at the PRs in this repo as much as the main Astro one. We'll be sure to mention you next time we LGTM, so you know it's good for you to merge!

[natemoo-re]

Thanks for the reminder ping @sarah11918! The upstream change for this has yet to be merged in, but I forgot to link it here. Will finish that PR and circle back when it's merged. Switching to draft for now.

[sarah11918]

@natemoo-re The corresponding Astro PR for this has been closed. Should we close this one too, and reopen if something happens with it upstream?

[delucis]

Seems fair to close this for now — we can reopen if the feature PR gets merged.