Introduce pluggable architecture with support for multiple registries

[jenna-winkler]

Description

This epic introduces a "pluggable" architecture to the framework, enabling the separation of configuration from code, leveraging YAML as a flexible and human-readable format, and implementing a registry/loader mechanism that supports multiple registries.

Motivation

Our primary motivation for adopting a pluggable architecture is to enhance reusability, extensibility, and ease of use. By decoupling configuration from code, we can:

• Reduce coupling between components, making it easier to modify or replace individual components without affecting others
• Improve maintainability through modular design, enabling faster development and fewer bugs
• Enhance flexibility in adding new features or integrations by allowing users to easily add or remove configurations
• Support both embedded and distributed deployment models without code changes
• Create a zero-friction transition between local development and platform deployment

Deliverables

The epic consists of these key deliverables:

1. Core plugin system and registry (plugin interface definition, registry implementation, plugin loading mechanism)
2. No-Code YAML Configuration (structure and format for YAML configuration files, templating system for prompting capabilities, support for various plugin types (chat models, agents, tools))
3. Reference Implementation (example implementation of the plugin architecture)
4. Clear documentation

[geneknit]

@terylt @Tomas2D can y'all break this down into sub-issues and add an estimate for delivery by Thursday?

[jenna-winkler]

closing in favor of smaller issues e.g. #938