parquet:Add file_extension for specify file_extension of ParquetReadOptions

[glfeng318]

Which issue does this PR close?

Rationale for this change

This allows users to specify the file extendsion in ParquetReadOptions

let opt = ParquetReadOptions::new().file_extension("").table_partition_cols(vec![("dt".as_str, DataType::Utf8)]);

What changes are included in this PR?

add a new fn file_extension for ParquetReadOptions

Are these changes tested?

tests covered by existing tests

Are there any user-facing changes?

[alamb]

Thank you @glfeng318 -- this looks like a nice improvement to me

[glfeng318]

cargo fmt check failed and i had removed the whitespace in line 270

[findepi]

Makes sense.

Curious, is the only use-case to set this to ""?

[glfeng318]

No,
in most case, file_extension is set by the defualt .parquet
and some framework/apps(in my case: hive) may generate parquet files without extension, so it was set to ""

[alamb]

Thanks again @glfeng318