Function to_flat_sst_arrow_schema 

pub fn to_flat_sst_arrow_schema(
    metadata: &RegionMetadata,
    options: &FlatSchemaOptions,
) -> SchemaRef

Gets the arrow schema to store in parquet.

The schema is:

primary key columns, field columns, time index, __prmary_key, __sequence, __op_type

Panics

Panics if the metadata is invalid.