docs: add workload identity options for replication

[RaphDal]

Summary

• Add tips for AWS S3 explaining that credentials can be omitted when using IAM roles (EC2 instance profile, EKS pod identity, ECS task role)
• Add tips for Azure Blob Storage explaining that account_key can be omitted when using Managed Identity
• Add tips for GCS explaining that credentials can be omitted when using Workload Identity or GCE VM with attached service account

Test plan

• Verify the documentation renders correctly with yarn start
• Confirm the admonition syntax displays properly

🤖 Generated with Claude Code

[github-actions]

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A component in src/components/ or src/theme/ was modified in this pull request.

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[github-actions]

🚀 Build success!

Latest successful preview: https://preview-356--questdb-documentation.netlify.app/docs/

Commit SHA: d7e37f6

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[sklarsa]

lgtm, thanks!