Handle latest version downloads programmatically

[mattlord]

Previews:

• https://deploy-preview-1855--vitess.netlify.app/docs/21.0/get-started/local/#install-vitess
• https://deploy-preview-1855--vitess.netlify.app/docs/20.0/get-started/local/#install-vitess
• https://deploy-preview-1855--vitess.netlify.app/docs/19.0/get-started/local/#install-vitess
• https://deploy-preview-1855--vitess.netlify.app/docs/18.0/get-started/local/#install-vitess

[netlify[bot]]

✅ Deploy Preview for vitess ready!

Name	Link
🔨 Latest commit	d4323bac82344a6ccbedf0260aa00888420abe05
🔍 Latest deploy log	https://app.netlify.com/sites/vitess/deploys/66f1b3aa1de397000879475f
😎 Deploy Preview	https://deploy-preview-1855--vitess.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.

[shlomi-noach]

Nice! Do you need someone (e.g. me) to actually try the sequence of commands on their machine?

[mattlord]

Nice! Do you need someone (e.g. me) to actually try the sequence of commands on their machine?

I did — and will again before merging — but others are welcome to as well.