feat: add default main.js to config that passes an empty object

This PR does the following:

Set up a default main.js that is consumed by Emulsify Core and gives an example of storybook config.

Related Issue(s)

None

Functional Testing:

[ ] Setup a new theme or add this file to an existing Emulsify 5.x project
[ ] Update Emulsify Core to 1.2.0

[ ] Uncomment the provided configOverrides and implement a config change. Example: add the following after the docs: {}

managerHead: (head) => `
${head}
<style>
  :root {
    --colors-emulsify-blue-100: #e6f5fc;
    --colors-emulsify-blue-200: #CCECFA;
    --colors-emulsify-blue-300: #99D9F4;
    --colors-emulsify-blue-400: #66c5ef;
    --colors-emulsify-blue-500: #33b2e9;
    --colors-emulsify-blue-600: #009fe4;
    --colors-emulsify-blue-700: #007FB6;
    --colors-emulsify-blue-800: #005f89;
    --colors-emulsify-blue-900: #00405b;
    --colors-emulsify-blue-1000: #00202e;
    --colors-purple: #8B1E7E;
  }
</style>
`,

[ ] Run npm run develop to startup storybook. Inspect the main <head> of the source and verify the inline styles defined above are now rendered on the page.

emulsify-ds / emulsify-drupal

feat: add default main.js to config that passes an empty object #321

Related Issue(s)

Functional Testing: