ClickStack: add ClickStack API reference docs

[Blargian]

Summary

Adds ClickStack API reference using https://github.com/PaloAltoNetworks/docusaurus-openapi-docs

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]

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Project	Deployment	Preview	Comments	Updated (UTC)
clickhouse-docs	Canceled			Nov 25, 2025 10:03am

2 Skipped Deployments

Project	Deployment	Preview	Comments	Updated (UTC)
clickhouse-docs-ru	Ignored	Preview		Nov 25, 2025 10:03am
clickhouse-docs-zh	Ignored	Preview		Nov 25, 2025 10:03am

[Blargian]

Locally have no issues with rendering but it breaks styling in the preview environment:

installHook.js:1 Docusaurus React Root onRecoverableError: Error: Minified React error #418; visit https://reactjs.org/docs/error-decoder.html?invariant=418 for the full message or use the non-minified dev environment for full errors and additional helpful warnings.
    at lg (16073.0d059ff5.js:1:47409)
    at i (16073.0d059ff5.js:1:122024)
    at oO (16073.0d059ff5.js:1:99977)
    at 16073.0d059ff5.js:1:95026
    at oS (16073.0d059ff5.js:1:95033)
    at O (53139.8ef9360a.js:1:2171)
    at MessagePort.P (53139.8ef9360a.js:1:2701) Object

[Blargian]

Closing in favor of #4789