Introduce Feast LLM Add-On

[franciscojavierarceo]

Is your feature request related to a problem? Please describe.

With #4364, #4890, and #4714, Feast is aiming to support NLP/LLMs as a first class citizen.

Other NLP related frameworks offer default transformations (e.g., formatting data via docling, llamaparse) and formatting data for ease of use in LLMs.

Feast should support this natively through an add on. The benefit of this add-on would be to allow users to have default libraries that can be used in offline training and online serving.

Describe the solution you'd like
To be scoped.

Describe alternatives you've considered
N/A

Additional context
https://docs.llamaindex.ai/en/stable/llama_cloud/llama_parse/
https://help.openai.com/en/articles/8868588-retrieval-augmented-generation-rag-and-semantic-search-for-gpts