[Roadmap] llm-d vLLM Simulator Roadmap

[mayabar]

This roadmap is subject to change and contributions are welcome!

https://docs.google.com/document/d/1ASTkYKFQEb0-XXQBs-1aGDPa22Ybu_GRYvrQPbK4ybI/edit?usp=sharing

[mayabar]

roadmap tasks status was updated in the document