Add pre-aggregates and NATS workers self-host docs

[mintlify]

Summary

• Added Pre-aggregates page (self-host/pre-aggregates) with Enterprise Plan and Helm chart badges, Helm values configuration, deployed components table, and scaling guidance
• Added NATS workers page (self-host/nats-workers) with Helm chart badge, setup instructions, and scaling configuration
• Both pages include a callout linking to the existing pre-aggregates reference for non-self-host users
• Added both pages to the "Self-hosting and deployment" navigation in docs.json

[github-actions]

🤖 Documentation Bot

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