Run `safe-settings` as a free app in Vercel like `probot/settings` (`repository-settings/app`)

## Prerequisites:

- maintainer (github) approval of this

## New Feature

The `probot/settings` app is very helpful since it does 90% of what I need. It doesn't do everything (autolinks, centralized default settings, etc) and that's where `github/safe-settings` fits nicely. Unlike `probot/settings`, `github/safe-settings` needs to be self-hosted.

Would you folks consider offering `github/safe-settings` as a free github app similar to [`probot/settings` app](https://github.com/apps/settings) in Vercel?

Thank you for a great app!