Fix SQL container throughput update to preserve existing throughput buckets

[Achint-Agrawal]

Description

Previously, updating SQL container throughput would reset existing throughput buckets to None when the -ThroughputBucketsObject parameter was not explicitly provided. This change preserves existing throughput buckets when the parameter is omitted, only removing them when explicitly set to an empty array.

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[YanaXu]

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[NoriZC]

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[NoriZC]

@Achint-Agrawal Please resolve the conflict ang fix the failed tests

[github-actions]

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[NoriZC]

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