Efficient storage for several INT_8 and INT_16

In very large datasets, aggregating several INT8 into INT32 fields (or byte array) can make a big difference.
In parquet, efficient algorithms exist for INT32, so if the LogicalType is INT_8 the encoded int might take up only one byte.

However further optimizations could be made by allowing the user to better specify the types.
What about BYTE_ARRAY logical type, backed by FIXED_LEN_BYTE_ARRAY type (or eventually INT_32)?

**Reporter**: [Fernando Pereira](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=ferdonline)

_{**Note**: *This issue was originally created as [PARQUET-845](https://issues.apache.org/jira/browse/PARQUET-845). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

Inizia esaminando come Parquet rappresenta attualmente i tipi logici INT8 e INT16 con INT32, quindi analizza il comportamento di codifica esistente per i valori INT32 e BYTE_ARRAY. L’attività è completata quando viene concordata una rappresentazione concreta del tipo e l’ottimizzazione dello storage proposta viene implementata e validata, ma l’issue non indica file o test da eseguire.

Scritto dal modello di indicizzazione a partire dal testo della issue.