CLI: Add prop-types dependency if not using TypeScript

[IanVS]

Issue:

We haven't been adding prop-types to React JS projects, even though the example components use it. This breaks in yarn pnp and pnpm.

What I did

If the detected language is JavaScript (not TypeScript), we'll add prop-types to the dependencies that are installed during storybook init.

How to test

• Is this testable with Jest or Chromatic screenshots?
• Does this need a new example in the kitchen sink apps?
• Does this need an update to the documentation?

If your answer is yes to any of these, please make sure to include it in your PR.

[benmccann]

thanks for fixing this!