[HUDI-3172] Refactor hudi existing modules to make more code reuse in V2 Implementation (#4514)

* Introduce hudi-spark3-common and hudi-spark2-common modules to place classes that would be reused in different spark versions, also introduce hudi-spark3.1.x to support spark 3.1.x.
* Introduce hudi format under hudi-spark2, hudi-spark3, hudi-spark3.1.x modules and change the hudi format in original hudi-spark module to hudi_v1 format.
* Manually tested on Spark 3.1.2 and Spark 3.2.0 SQL.
* Added a README.md file under hudi-spark-datasource module.

hudi-spark-datasource/hudi-spark3.1.x/src/main/resources/META-INF/services/org.apache.spark.sql.sources.DataSourceRegister

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