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.*}

首先检查 Parquet 目前如何使用 INT32 表示逻辑类型 INT8 和 INT16，然后检查现有的 INT32 和 BYTE_ARRAY 值编码行为。在就具体的类型表示达成一致，并实现和验证所提议的存储优化后，即可视为完成，但 issue 没有指定要运行的文件或测试。

由索引模型根据 Issue 内容生成。