Add extension-system docs

[costrouc]

Reference Issues or PRs

Closes #349

What does this implement/fix?

Put a x in the boxes that apply

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds a feature)
• Breaking change (fix or feature that would cause existing features not to work as expected)
• Documentation Update
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build related changes
• Other (please describe):

Testing

• Did you test the pull request locally?
• Did you add new tests?

Documentation

Access-centered content checklist

Text styling

• The content is written with plain language (where relevant).
• If there are headers, they use the proper header tags (with only one level-one header: H1 or # in markdown).
• All links describe where they link to (for example, check the Nebari website).
• This content adheres to the Nebari style guides.

Non-text content

• All content is represented as text (for example, images need alt text, and videos need captions or descriptive transcripts).
• If there are emojis, there are not more than three in a row.
• Don't use flashing GIFs or videos.
• If the content were to be read as plain text, it still makes sense, and no information is missing.

Any other comments?

[netlify]

✅ Deploy Preview for nebari-docs ready!

Name	Link
🔨 Latest commit	09368ea
🔍 Latest deploy log	https://app.netlify.com/sites/nebari-docs/deploys/64db6cc3455cde000889b9d1
😎 Deploy Preview	https://deploy-preview-352--nebari-docs.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 configuration.

[iameskild]

My one question is whether this belongs in the how-to, developer, or architecture section? @pavithraes do you have a opinion one way or another?

Other than that, awesome work! Thanks @costrouc!

[costrouc]

@iameskild currently I have it in the howtos. @pavithraes is this the right one?

[pavithraes]

Thanks, @costrouc! I think it fits well in the how-to guide. :)