Feat: add bucket encryption enforcement configuration

[thiyaguk09]

Description

This PR implements support for Bucket Encryption Enforcement in the BucketMetadata interface. This feature allows users to restrict object creation based on specific encryption types (Google-managed, Customer-managed, or Customer-supplied).

Key Changes:

• Added googleManagedEncryptionEnforcementConfig, customerManagedEncryptionEnforcementConfig, and customerSuppliedEncryptionEnforcementConfig to the BucketMetadata interface.
• Included the server-generated effectiveTime (readonly) and restrictionMode fields for each configuration type.
• Added three new code samples: setBucketEncryptionEnforcementConfig, getBucketEncryptionEnforcementConfig, and removeAllBucketEncryptionEnforcementConfig.

Impact

This is a non-breaking feature addition. It enables security-conscious users to enforce CMEK-only (Customer-Managed Encryption Keys) policies at the bucket level, aligning the Node.js library with the latest GCS API capabilities.

Testing

• Unit Tests: Added coverage in test/bucket.ts to verify that metadata is correctly serialized into PATCH requests. All tests follow the recommended pattern of mocking the underlying request layer.
• System Tests: Added new test cases in system-test/storage.ts that execute the sample scripts against a live GCS project to verify end-to-end functionality and backend state persistence.
• Samples: Verified that all three new samples run successfully and produce human-readable output.

Additional Information

Note that effectiveTime is treated as a read-only field populated by the server, which is verified in the system tests.

Checklist

• Make sure to open an issue as a bug/issue before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
• Ensure the tests and linter pass
• Code coverage does not decrease
• Appropriate docs were updated
• Appropriate comments were added, particularly in complex areas or places that require background
• No new warnings or issues will be generated from this change

Fixes #🦕

[snippet-bot]

Here is the summary of changes.

You are about to add 3 region tags.

• samples/getBucketEncryptionEnforcementConfig.js:23, tag storage_get_encryption_enforcement_config
• samples/removeAllBucketEncryptionEnforcementConfig.js:23, tag storage_remove_all_encryption_enforcement_config
• samples/setBucketEncryptionEnforcementConfig.js:26, tag storage_set_encryption_enforcement_config

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