feat(agentic chat): Implement MCP server management with UI

[abeatrix]

This commit introduces the ability to manage Model Context Protocol (MCP) servers directly within the VS Code extension. It includes features for adding, removing, enabling, and disabling MCP servers, along with displaying their status and associated tools.

Key changes:

• Adds configuration options for MCP servers in VS Code settings (cody.mcpServers).
• Implements MCP server connection management, including adding, removing, and updating server configurations.
• Introduces a new "MCP Servers" settings view in the Cody panel for managing servers.
• Integrates MCP tools into the agentic chat workflow, allowing Cody to utilize tools exposed by MCP servers.
• Updates the @anthropic-ai/sdk dependency to ^0.39.0.
• Adds support for image content in MCP tool results.
• Improves error handling and logging for MCP server connections and tool execution.
• Adds commands for managing MCP servers via the command palette.

These changes enable users to leverage external tools and resources within Cody, enhancing its capabilities and integration with other systems.

Test plan

Try add a MCP server via the new UI component and ask agentic chat to use the tool to confirm it's working