New 'cloud_credential_error' classification for Google Cloud credential failures

What

• A new error category, cloud_credential_error, is added for Google Cloud credential failures, alongside the existing AWS-specific wif_credential_error.
• A new check inspects an error and reports which cloud provider, AWS or Google Cloud, a credential failure came from, setting an isCloudCredentialError flag on API-error objects when it fires.
• The generic API error classifier now returns cloud_credential_error for these cases, separate from the existing rate_limit, authentication_failed, and server_error buckets, and treats it as non-fatal like other similar categories.
• A new account-blocking state maps to this case with the message "cloud credentials unavailable — check or refresh them", and cloud_credential_error is also recognized as an abort/error reason throughout the relevant classification and error-code mapping logic.
• Documentation describing this error handling was widened from "AWS credential-expiry error" to "AWS / Google Cloud credential failure".

Why Previously a Google Cloud credential problem might have been lumped in with generic authentication failures, making it harder to tell what actually went wrong. Now it's classified distinctly so error messages and handling can point specifically at cloud credential issues.