docs: add best practices doc for third-party syncing

[shahednasser]

Summary

What — What changes are introduced in this PR?

Add a best practices doc for syncing data between Medusa and external services

Closes DX-2351

Why — Why are these changes relevant or necessary?

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How — How have these changes been implemented?

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Testing — How have these changes been tested, or how can the reviewer test the feature?

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Examples

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// Example usage

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Checklist

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• The changes are covered by relevant tests
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Additional Context

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Project	Deployment	Preview	Comments	Updated (UTC)
docs-v2	Ready	Preview	Comment	Dec 3, 2025 11:53am

7 Skipped Deployments

Project	Deployment	Preview	Comments	Updated (UTC)
api-reference	Ignored			Dec 3, 2025 11:53am
api-reference-v2	Ignored			Dec 3, 2025 11:53am
cloud-docs	Ignored			Dec 3, 2025 11:53am
docs-ui	Ignored			Dec 3, 2025 11:53am
medusa-docs	Ignored			Dec 3, 2025 11:53am
resources-docs	Ignored			Dec 3, 2025 11:53am
user-guide	Ignored			Dec 3, 2025 11:53am

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Latest commit: 2660e7c

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