Document the guide for SecretManagerSecretVersion API (Legacy to Direct)

[yuwenma]

Checklist

• I did not find a related open enhancement request.
• I understand that enhancement requests filed in the GitHub repository are by default low priority.
• If this request is time-sensitive, I have submitted a corresponding issue with GCP support.

Describe the feature or resource

We should give clear user guide on the expected behavior for the stale, legacy and deprecated SecretManagerSecretVersion APIs.
spec.deletionPolicy --> delete-policy annotation
spec.IsSecretDataBase64 --> This is encrypted in k8s already
status.version --> Correct the doc because this is a status field and no deprecation.

Additional information

No response

Importance

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