Retrieve overall usage statistics

### Describe the feature or problem you'd like to solve

It would be nice to have a way to programmatically retrieve usage statistics for your user, similar to the small overview that the VSCode plugin gives in the bottom right corner. This is different from the `/usage` command, which reports on the stats of the current session.

### Proposed solution

Having something like `copilot usage [options]` could provide a nice entry point for integrating this information with other tools. It could even support `--json` to output the information in JSON format for better parsing.

People could then integrate this information in their statusbars, in a editor plugin, terminal prompt, whatever.

### Example prompts or workflows

_No response_

### Additional context

_No response_