Feature: auto-detect Prettier as a post-processor in CLI

[JoshuaKGoldberg]

🚀 Feature Request

In the npx typestat getting started CLI that generates a typestat.json, if a Prettier configuration is detected, it should offer to add it as a post-processor.

Existing Behavior

Mutators don't generally put effort into respecting Prettier settings. As a result, auto-fixed code often would not pass Prettier.

Change Proposal

"Hey, would you like to have Prettier run on mutated files?"