added mlforecast contrib

[zilto]

[Summary of contribution]
Added a contrib to train ML models for forecasting using Nixtla's mlforecast

For new dataflows:

Do you have the following?

• Added a new folder for my dataflow under my username directory.
  • Added a README.md file under my dataflow directory that follows the standard headings and is filled out.
  • Added a init.py file under my dataflow directory that contains the Hamilton code.
  • Added a requirements.txt under my dataflow directory that contains the required packages outside of Hamilton.
  • Added tags.json under my dataflow directory to curate my dataflow.
  • Added valid_configs.jsonl under my dataflow directory to specify the valid configurations.
  • Added a dag.png that shows one possible configuration of my dataflow.

For existing dataflows -- what has changed?

How I tested this

There is a notebook run.ipynb that calls all available variables and should run from start to finish.

Notes

Checklist

• PR has an informative and human-readable title (this will be pulled into the release notes)
• Changes are limited to a single goal (no scope creep)
• Code passed the pre-commit check & code is left cleaner/nicer than when first encountered.
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Dataflow documentation has been updated if adding/changing functionality.

[sweep-ai]

Apply Sweep Rules to your PR?

• Apply: Leftover TODOs in the code should be handled.
• Apply: All new business logic should have corresponding unit tests in the tests/ directory.
• Apply: Any clearly inefficient or repeated code should be optimized or refactored.

[elijahbenizzy]

LGTM! A few small comments on wording/docs.