Exclude GA tag manager from preview deployments

[Blargian]

Summary

Currently GA tag manager is included in preview deployments.
Added an environment variable to preview vercel deployment only called VERCEL_PREVIEW
Modified Docusaurus.config.js files to not include the GA tag manager plugin if this environment variable is detected.

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]

@Blargian is attempting to deploy a commit to the ClickHouse Team on Vercel.

A member of the Team first needs to authorize it.

[vercel]

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

Project	Deployment	Preview	Comments	Updated (UTC)
clickhouse-docs	Ready	Preview		Oct 6, 2025 8:42am

2 Skipped Deployments

Project	Deployment	Preview	Comments	Updated (UTC)
clickhouse-docs-ru	Ignored	Preview		Oct 6, 2025 8:42am
clickhouse-docs-zh	Ignored	Preview		Oct 6, 2025 8:42am

[Copilot]

Pull Request Overview

Excludes Google Analytics tag manager from preview deployments by conditionally including the googleTagManager plugin based on the VERCEL_PREVIEW environment variable.

• Replaces gtag with googleTagManager plugin in all language configurations
• Adds conditional logic to exclude GA tracking from Vercel preview deployments
• Updates container ID from tracking ID to Google Tag Manager container ID

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
docusaurus.config.zh.js	Updates Chinese config to conditionally include GTM based on preview environment
docusaurus.config.ru.js	Updates Russian config to conditionally include GTM based on preview environment
docusaurus.config.jp.js	Updates Japanese config to conditionally include GTM based on preview environment
docusaurus.config.en.js	Updates English config to conditionally include GTM based on preview environment

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}