adding Holistics.io to ClickHouse docs

[growth-holistics]

Summary

Holistics customers couldn't find instructions for ClickHouse integration with Holistics on Clickhouse docs so we added the instructions here.

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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[CLAassistant]

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