CLI Configuration for Typegen

[okj579]

Is your feature request related to a problem? Please describe.
Using Typegen across separate repositories (e.g. on for studio, one for the frontend) is difficult, as you can't mix local settings and those that are committed to the repository. The only configuration possibility at the moment is sanity-typegen.json.

Describe the solution you'd like
Configuration via CLI options and/or environment variables

Describe alternatives you've considered
I'm using an external script at the moment to gather the relevant options from constant, project and local settings, then resolve paths to be relative to the Sanity Studio root, write a temporary sanity-typegen.json, run typegen and clean up again afterwards. This is much more cumbersome than it has to be, though.