[SDG] Add Mapping Synthetic Data Generator

[IanHoang]

Please provide details on how and where the documentation can be improved

This is the in-house synthetic data generator that OSB comes packaged with. It should be able to take in any OpenSearch index mapping and generate synthetic documents based off of it. Users should have some control over how data is generated. But for very detailed and niche ways of how the data is generated, users should use the custom synthetic data generator.

Related to #764