Update Project Roadmap Documentation

The project roadmap documentation needs more clarity to help answer questions that come up such as:

• what is the future of Orchestrator going to look like
• what will it support
• how does it fit into various deployment scenarios

A minimal definition of done:

• updated mermaid chart showing the decoupled pieces in a way that is clearer than the original proposal
• Updated main README page that is more concise and has better organization