Adding HDFS support for data generation

[bilalbari]

This PR contains the following changes -

1. Adding DbGen class for running data generation as part of mapper
2. Updating build files for the same
3. Changes to README
4. Changes to existing python files for supporting HDFS data generation

[gerashegalov]

Note that beyond subpar user-perceived delays with shelling out to launch heavy JVMs, we hit limitations in the past where hadoop CLI is not available. If we document that this script can be launched via spark-submit than we can use PY4J NVIDIA/spark-rapids#10599

On the other hand why do we need to wrap a Java program in Python CLI to begin with?

[bilalbari]

The java program is a mapper triggered only when generating data for hdfs. In case of local data generation, the python wrapper does not trigger a mapreduce job.
For the missing hadoop cli, there is a primary check in the python program triggering install hadoop cli message just for verbosity.
Here the hadoop job is just creating a limiting set of directories ( 8 in total - 1 per nds-h table) and moving nds-h generated data to the required folders.
Currently this is not being triggered via spark-submit.

[wjxiz1992]

This is more like a tech debt. When initializing this project, the order was to use Python and void the one that DB is using. I argued that time that we can also use Scala but failed.

More details I can recall, to avoid the way that we chain call "python-hdfs", the best option was to leverage the

_FILTER =  [Y|N]         -- output data to stdout

argument to pipe text output to stdout then pipe it directly into Spark Dataframe. (This is also what DB does) In this way we don't need any hadoop job to help generate distributed dataset.

Unluckily, latest TPC-DS v.3.20 disabled this argument, and the order was to use latest version and try our best not to modify it.

Thus it becomes what it is now.

[bilalbari]

As per allen's comment, I can pick this up as a separate issue later to figure out if there is any alternate solution to avoid chaining hadoop commands from python.