Improve Documentation on Beacon Node API Flow and Debugging

[boulder225]

🎯 Problem to be solved

The documentation at https://docs.obol.tech/ lacks detailed information on understanding and debugging the API flow of different beacon node implementations.

🛠️ Proposed solution

Taking inspiration from the Runbook:

• For major beacon node implementations (Lighthouse, Prysm, Teku), create dedicated sections explaining API flow and internals
• Cover how beacon node processes API endpoints, steps in handling requests, common errors, debugging practices
• Provide code examples and diagrams illustrating API flow and component interactions
• Include troubleshooting guides and FAQs specific to each implementation, with step-by-step instructions
• Maintain documentation updates as new beacon node versions are released