Support custom-endpoint in sidecar mounter

[uriel-guzman]

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[gemini-code-assist]

Code Review

This pull request introduces support for a custom endpoint in the GCS Fuse CSI driver sidecar mounter. Changes include updating the ServiceManager interface and its implementations to accept a customEndpoint parameter, which is then used when initializing the storage client. A review comment highlights that the custom endpoint should also be applied to the control client to ensure consistency during the pre-mount phase.

[gemini-code-assist]

The customEndpoint is currently only applied to the storageClient. However, the controlClient (initialized at line 476) is used for the CheckBucketExists call during the sidecar's pre-mount phase. If a custom endpoint is required for storage access, it is highly likely that the Storage Control API also needs to be directed to a corresponding custom endpoint. Failing to set this will cause the CheckBucketExists call to attempt to reach the default Google Cloud endpoints, which may fail or be blocked in restricted environments.

Suggested change

	if customEndpoint != "" {
	storageOpts = append(storageOpts, option.WithEndpoint(customEndpoint))
	}
	if customEndpoint != "" {
	storageOpts = append(storageOpts, option.WithEndpoint(customEndpoint))
	controlOpts = append(controlOpts, option.WithEndpoint(customEndpoint))
	}