fix(storage): enable storage features when using default GCS endpoint

[marevol]

Summary

The admin UI's storageEnabled flag previously required a non-blank storage.endpoint, which hid storage-dependent features (e.g. thumbnail/asset storage admin links) whenever GCS was used with the default storage.googleapis.com host. This change recognizes GCS-with-default-endpoint as a valid enabled configuration and stops GcsStorageClient from treating the default host as a custom endpoint.

Changes Made

• SystemHelper: extracted a new isStorageEnabled(FessConfig) helper. Storage is now enabled when storage.bucket is set AND either storage.endpoint is non-blank or storage.type is gcs (case-insensitive). setupStorageInfo delegates to this helper.
• GcsStorageClient:
  • Added isDefaultEndpoint(String) to detect the default GCS host (storage.googleapis.com, HTTPS, default port). Custom-host/NoCredentials overrides are now skipped when the configured endpoint matches the default, so real Google credentials are used.
  • Added a protected no-arg constructor so subclasses can override behavior without instantiating the underlying GCS client; close() short-circuits when storage is null.
• Tests:
  • SystemHelperTest#test_isStorageEnabled covers S3-with-endpoint, GCS-without-endpoint (both cases), unrelated type, missing bucket, and null config.
  • New GcsStorageClientTest#test_isDefaultEndpoint covers bare host, scheme/path variants, explicit default port, plus negative cases (HTTP, non-default port, hostname embedded in path).

Testing

• mvn test -Dtest=SystemHelperTest
• mvn test -Dtest=GcsStorageClientTest

Breaking Changes

None. The previous behavior is preserved whenever an explicit endpoint is configured; only the GCS-default-endpoint case becomes "enabled" instead of "disabled".

Additional Notes

• The default-endpoint detection deliberately matches only HTTPS on the default port so that fake-gcs-server / emulator configurations (typically HTTP and/or a custom port) continue to receive NoCredentials and the host override.
• isStorageEnabled is intentionally null-safe so callers don't have to guard against an uninitialized FessConfig.