Enhance TUF Documentation with Architecture Diagrams and Visual Aids

Description of issue or feature request:
We need to enhance the documentation for The Update Framework (TUF) by adding architecture diagrams and other visual aids, aligning with the CNCF TechDocs Assessment criteria. These additions should be similar to those found in Kubernetes and Falco documentation to improve understanding and clarity for users and contributors.

Current behavior:
The current documentation for TUF lacks detailed architecture diagrams and visual representations, making it challenging for users to grasp the system's design and components easily.

Expected behavior:
We expect to see the addition of comprehensive architecture diagrams and other visual aids in the TUF documentation, similar to the ones found in Kubernetes and Falco documentation. These diagrams should clearly illustrate the system's architecture, key components, data flow, and interactions, providing an intuitive understanding of TUF's workings.

No documentation files, tests, or entry points are specified. Start by reviewing the existing TUF documentation against the linked CNCF TechDocs criteria and the Kubernetes and Falco examples. Done means the documentation includes agreed architecture diagrams and visual aids covering TUF’s components, data flow, and interactions.