add ClickPipes docs for planetscale for postgres source

[heavycrystal]

Summary

Checklist

• Delete items not relevant to your PR
• URL changes should add a redirect to the old URL via https://github.com/ClickHouse/clickhouse-docs/blob/main/docusaurus.config.js
• If adding a new integration page, also add an entry to the integrations list here: https://github.com/ClickHouse/clickhouse-docs/blob/main/docs/integrations/index.mdx

[vercel]

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

Project	Deployment	Preview	Comments	Updated (UTC)
clickhouse-docs	Ready	Preview	Comment	Aug 20, 2025 4:08pm
clickhouse-docs-jp	Building	Preview	Comment	Aug 20, 2025 4:08pm

2 Skipped Deployments

Project	Deployment	Preview	Comments	Updated (UTC)
clickhouse-docs-ru	Ignored	Preview		Aug 20, 2025 4:08pm
clickhouse-docs-zh	Ignored	Preview		Aug 20, 2025 4:08pm