add react18 + webpack5 template

[ndelangen]

Add a template for testing: a custom react app using webpack 5 (react18 + ts)

[tmeasday]

@ndelangen OK, so the issue here is that the preview webpack config includes:

    fallback: {
      path: '/Users/tom/GitHub/storybookjs/storybook/sandbox/react-webpack-18-ts/node_modules/path-browserify/index.js',
      assert: false,
      util: 'util',
      crypto: false
    },

Notice assert: false.

I'm not sure why that's the case in this setup (but not say CRA). It's some interaction between this line:

storybook/code/lib/builder-webpack5/src/preview/iframe-webpack.config.ts

Line 261 in e095e8f

assert: require.resolve('browser-assert'),

and this one

storybook/code/lib/builder-webpack5/src/preview/base-webpack.config.ts

Line 94 in e095e8f

assert: false,

You no doubt understand better than me the precedence between the two.

I'm not sure why the second one exists, but given it is for this PR that is about the manager, I think it can likely be deleted.

[ndelangen]

@storybookjs/core we need to clean up the webpack config resolution mechanism for 7.0 as part of our breaking changed roadmap.