Documentation and Testing of Driver Plugin System

[unsuman]

Description

Write detailed technical documentation on the plugin architecture and protocol. Provide a comprehensive implementation guide and template code for plugin developers. Create user documentation for plugin usage and management.

Testing and Integration:

• Develop integration tests for the plugin subsystem across different environments.
• Ensure compatibility and stability with both built-in and external plugins.

[AkihiroSuda]

Removing gsoc/2025 label, as the end of the term is approarching

[AkihiroSuda]

Update Makefile variable usage, explain the concept of internal and external drivers under experimental in dev's guide/internal data structure. Any other docs update that is needed?

Originally posted by @unsuman in #3925