Inject storybook environment variables

[IanVS]

Fixes #104.

This injects storybook environment variables through the define config of vite, similar to what the webpack builder does using the DefinePlugin. I needed to create a customized version of one of the core storybook functions, since it assumes that process.env is going to be used, whereas with vite we use import.meta.env.

I also added example stories in react, vue, and svelte (my first time writing vue and svelte!). They're ugly, but they show that the STORYBOOK environment variable is being provided correctly (it wasn't previously).

Before:

After:

[eirslett]

Do we risk exposing process.env.SUPER_SECRET_PASSWORD if that is somehow set up as an environment variable on the server?

[IanVS]

No, because storybook only finds variables starting with STORYBOOK_. That's why I'm using preset.apply("env").

[FezVrasta]

environment variables starting with VITE_ are not being injected into the production builds, only ones starting with STORYBOOK_ are. Also STORYBOOK is missing too. Is this expected?

[IanVS]

@FezVrasta I responded to your issue: #489