[legacy-framework] Convert app template Jest config to TypeScript

[ratson]

What are the changes and their implications?

This enables code completion.

Feature Checklist

• Integration test added (see test docs if needed)
• Documentation added/updated (submit PR to blitzjs.com repo)

[flybayer]

Thanks @ratson! This seems reasonable for TS users. However, as is, this breaks support for JS users (blitz new myapp --js). You'll need to take the same approach here as we do for jsconfig.json and tsconfig.json

[ratson]

@flybayer Updated to support JS config.

[flybayer]

Awesome, thank you!!

[blitzjs-bot]

Added @ratson contributions for code