Parallel replicas

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Summary

Adds parallel replicas page. Images to be replaced by ones from design. (In progress)

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/en/integrations/index.mdx

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@tom-clickhouse tagging for review when you get a chance, as discussed in standup. https://clickhouse-docs-roxajk5r6-clickhouse.vercel.app/docs/en/deployment-guides/parallel-replicas. Images will be polished by design, the request is in progress.