Update database-migration-service.md

[abhims14]

Adding BC limitation

[prmerger-automator]

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[learn-build-service-prod]

Learn Build status updates of commit 8d613c6:

⚠️ Validation status: warnings

File	Status	Preview URL	Details
data-migration/sql-server/managed-instance/database-migration-service.md	⚠️Warning		Details

data-migration/sql-server/managed-instance/database-migration-service.md

• Line 422, Column 14: [Warning: file-not-found - See documentation] Invalid file link: 'managed-instance-link-migrate.md'.

For more details, please refer to the build report.

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