Support import, export, and backup of Chat sessions across workspaces in VSCode Copilot

I would like the ability to export, import, and back up VS Code Chat sessions.

Chat sessions currently appear to be associated with a specific project folder or workspace. When the project folder is moved or opened from another location, the existing chat sessions can no longer be accessed.

It would be helpful to provide:
- An option to export selected or all chat sessions to a file.
- An option to import previously exported chat sessions into another workspace.
- A backup and restore option for chat history.
- The ability to retain chat sessions when a project folder is renamed or moved.

This would allow users to preserve important troubleshooting context, implementation decisions, prompts, and responses, while also making it easier to continue work across different projects or machines.