Add methods for persisting generated data

[ghanse]

Proposed changes

This PR introduces methods for writing generated data to output tables or files. Users will create an OutputDataset which specifies how data should be persisted:

gen = dg.DataGenerator(...)

output_dataset = OutputDataset(
  location="main.demo.table",
  output_mode="append",
  format="delta",
  options={"mergeSchema": "true"}
)

gen.buildOutputDataset(output_dataset)

Users can write to tables or files. Data can be built in batch or streaming mode:

gen = dg.DataGenerator(...)

output_dataset = OutputDataset(
  location="/Volumes/main/demo/files/demo_json",
  output_mode="append",
  format="json"
  trigger={"processingTime": "1 SECOND"}  # Optional streaming trigger
)

gen.buildOutputDataset(output_dataset, withStreaming=True)

I have also simplified the Pull Request template.

Resolves #343

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[anupkalburgi]

LGTM thanks!