Create a design document for implementing a podman plugin system.

We need to determine what types of plugins should be created and what it takes to satisfy user requirements. This design document should largely be based on satisfying use cases. We need to define those use cases as part of this work. We are also thinking that it might be interesting to convert some commands in podman into plugins like podman machine or quadlets or compose.

Acceptance Criteria

_Fill out design doc template: https://docs.google.com/document/d/1vrnvE_S-ujwE8JvxbtQhQA5eFz6wI6hjY7h40D4H_nU/edit?usp=sharing_