feat(azure-china): support azure china vault backend endpoint

[harshktpa]

Description

This PR introduces modifications to the Azure Key Vault backend to support Azure China. It enhances the GetSecrets and GetIndividualSecret methods to dynamically adjust the vault URL based on the environment specified in the AVP_AZ_CLOUD_NAME environment variable.

Fixes: #672 (support azure china cloud vault backend endpoint)

Checklist

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Type of Change

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• New tests
• Build/CI related changes
• Documentation content changes
• Other (please describe)

Other information

Other information
These changes allow the Azure Key Vault backend to function correctly in both standard Azure and Azure China environments by using the AVP_AZ_CLOUD_NAME environment variable. The logic for constructing the vault URL is updated, and the methods now handle secret retrieval based on the specified azure cloud environment.