[Bugfix] Source should throw exception when data types between StarRocks and Flink mismatch

[banmoy]

What type of PR is this：

• bugfix
• feature
• enhancement
• refactor
• others

Which issues of this PR fixes ：

Fixes #126

Problem Summary(Required) ：

Source connector will receive data in arrow format from StarRocks' BE, and data will be converted to Flink's format according to the type mapping between StarRocks and Flink. In StarRocksSourceFlinkRows#genFlinkRows, DataTypeUtils.map will be used to map StarRocks's type to Flink's type. It use the arrow's MinorType rather than StarRocks' native type. From the row_batch.cpp#convert_to_arrow_type, we can find that StarRocks's native VARCHAR and CHAR will both be converted to arrow's StringType in C++ or MinorType.VARCHAR in Java. So if arrow returns a MinorType.VARCHAR, we can't distinguish it's StarRocks' CHAR or VARCHAR, and DataTypeUtils.map will always map MinorType.VARCHAR to Flink's LogicalTypeRoot.VARCHAR. So if a column whose StarRocks's type is CHAR and Flink's type is VARCHAR, source should throw an exception to tell type incompatibility, but now it can work. We need fix it.

Checklist:

• I have added test cases for my bug fix or my new feature
• I have added user document for my new feature or new function