docs: where clause limitations with feature request CTA.

[thruflo]

Partly addresses https://github.com/electric-sql/electric/issues/1769 although it would be much better to add more technical details.

https://deploy-preview-1773--electric-next.netlify.app/docs/guides/shapes#where-clause

[netlify[bot]]

✅ Deploy Preview for electric-next ready!

Name	Link
🔨 Latest commit	0e390564dc65ef1756f10e500bcc05aaeac97829
🔍 Latest deploy log	https://app.netlify.com/sites/electric-next/deploys/66fe948c475eb800089dac4e
😎 Deploy Preview	https://deploy-preview-1773--electric-next.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.

[alco]

@thruflo given the small subset of SQL we support in shape where clauses, I believe it is more helpful to talk about what is supported, first and foremost. I have pushed a commit to that effect to your branch.