Support/generate shell completions for fig

### Is your feature request related to a problem? Please describe.

Rider and other tools use the [`fig`](https://github.com/withfig/autocomplete) definitions for CLI tools to power their enhanced autocompletions in a shell-agnostic way, These definitions are per-tool and currently can drift with new features/additions to the CLI.

### Describe the solution you'd like
We should implement a generator/exporter for the fig format for the [dotnet tools](https://github.com/withfig/autocomplete/blob/c180bb7cd0843960007c4500f98edd1fcc6d8086/src/dotnet.ts) and work with the maintainers to create a process for updates.