GitHub Copilot Marketplace Integration and Enterprise Support

### Describe the feature

## Description

Extend the Agent Toolkit for AWS to support GitHub Copilot Marketplace integrations, enabling developers to discover, install, and use marketplace-provided Copilot extensions, agents, MCP servers, and tools directly within Agent Toolkit workflows.

The goal is to ensure that developers using GitHub Copilot can seamlessly leverage marketplace capabilities alongside the existing toolkit without requiring custom integration work. This would allow Agent Toolkit projects to take advantage of the growing ecosystem of Copilot-powered tools and agents while maintaining a consistent developer experience.

An implementation is available in the following fork/branch:

- [Copilot Support Branch](https://github.com/stuartjsmith/agent-toolkit-for-aws/tree/copilot-support)

## Proposed Requirements

- Support GitHub Copilot Marketplace extensions and agents.
- Enable discovery and configuration of marketplace-provided capabilities.
- Allow marketplace agents and tools to participate in Agent Toolkit workflows.
- Support authentication and authorization models required by GitHub Copilot integrations.
- Provide a consistent developer experience across VS Code, GitHub Copilot, and Agent Toolkit components.
- Document supported marketplace capabilities, setup, and usage examples.

## Expected Benefits

- Expands interoperability with the GitHub Copilot ecosystem.
- Reduces integration effort for developers adopting marketplace agents and tools.
- Increases flexibility and extensibility of Agent Toolkit solutions.
- Enables faster adoption of new AI capabilities as they become available through the GitHub Copilot Marketplace.

## Additional Context

GitHub Copilot is becoming the primary AI-assisted development experience for many engineering teams. Supporting GitHub Copilot Marketplace integrations would allow Agent Toolkit users to take advantage of the rapidly growing ecosystem of Copilot extensions, agents, and MCP-based capabilities without leaving their existing workflows.

### Use Case

## Why is this needed?

GitHub Copilot has a growing ecosystem of marketplace extensions, agents, and MCP servers.

Adding support for GitHub Copilot Marketplace would allow Agent Toolkit users to easily leverage these capabilities without building custom integrations, improving interoperability and giving developers access to a wider range of AI-powered tools and workflows.

### Proposed Solution

_No response_

### Other Information

_No response_

### Acknowledgements

- [ ] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

Start by reviewing the requirements in this issue and the linked copilot-support branch, then identify the Agent Toolkit entry points involved in marketplace discovery, configuration, workflows, authentication, and documentation. Done means supported GitHub Copilot Marketplace capabilities are integrated consistently, authenticated, usable in workflows, and documented with setup and usage examples.

Written by the indexing model from the issue text.