Add an option for making requested schema case insensitive while reading

For projects such as hive and spark-sql which use parquet, the schema of the stored tables is always lowercase (because of limitations of hive metastore). It would be great if we can have a configurable option to read data from parquet irrespective of the case of the requested schema , supplied via ReadContext object.

**Reporter**: [Yash Datta](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=saucam) / @saucam

_{**Note**: *This issue was originally created as [PARQUET-304](https://issues.apache.org/jira/browse/PARQUET-304). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

首先定位 ReadContext 对象和 parquet schema 读取路径，然后检查请求的字段名如何与存储的名称进行匹配。定义可配置的不区分大小写行为，并通过测试进行验证，测试应涵盖大小写混合的请求 schema 与全小写的存储 schema 的情况。

由索引模型根据 Issue 内容生成。