Add MCP elicitation support

[mattzcarey]

Enable human-in-the-loop workflows for MCP tools by supporting the elicitation protocol. This allows MCP servers to request user input via forms during tool execution.

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• [FEATURE]: Plugin Support for Modal Human-in-the-loop Interactions  #5147: Plugin Support for Modal Human-in-the-loop Interactions - Requests ability for plugins to show modals and collect user input, which is closely related to MCP elicitation protocol functionality
• [FEATURE]: Generic UI Intent Channel for cross-client plugin-driven UX #6330: Generic UI Intent Channel for cross-client plugin-driven UX - Proposes a declarative UI system for forms, confirmations, and progress indicators that could serve as the foundation for MCP elicitation support

Feel free to ignore if your specific case addresses something unique to MCP servers themselves.