Have writer return parsed `ParquetMetadata`

[jonathanc-n]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

In my discussion with @liurenjie1024 in apache/iceberg-rust#960 and apache/iceberg-rust#1004, we found that ArrowFileReader returns ParquetMetadata while AsyncFileWriter is returning the unparsed thrift definition of the parquet metadata.

Describe the solution you'd like

Either change the writer to return ParquetMetadata instead of the thrift definition. Or implement a new writer to return the ParquetMetadata