Suppress file-level key-value metadata

For VOParquet files, each leaf parquet file *may* contain the same VO metadata inside the file-level metadata. This is plain text, and has the potential to be large.

The metadata should be present in `_common_metadata` and `_metadata` files, however, and can be cached on the client side. It would be helpful to (optionally) suppress sending that additional metadata over the wire.

No files or tests are named. Start by locating the server path that reads VOParquet leaf-file metadata and sends it over the wire, then inspect how `_common_metadata` and `_metadata` are handled. Done means an optional setting suppresses the repeated file-level metadata while preserving the shared metadata behavior.

Written by the indexing model from the issue text.