Docs: add warning about use of cache dictionary layouts in Cloud

[Blargian]

Summary

Together with ClickHouse/ClickHouse#102288 closes #5993

Since we use autoscaling in cloud, nodes can be replaced at any moment and if a node is replaced the dictionary is wiped clean. This can result in ingestion issues if they are using a dictionary to denormalize data in an MV. tl;dr only use complex key hashed or another dictionary lay out that prepopulates dictionaries, instead of populating them via caching mechanisms. See https://clickhouse.com/docs/dictionary/best-practices for more info on choosing dicationary cache layouts.

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

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Project	Deployment	Actions	Updated (UTC)
clickhouse-docs	Ready	Preview	Apr 9, 2026 8:09pm