[DO NOT MERGE] Set up source map to connect with local server

[alexvuong]

Description

This PR provides guide to create a custom webpack to generate source map files that will allow connection with local server for a MRT production debugging.

1. installed webpack and related packages (see the diff in package.json in this PR) in your root project
2. Add a webpack customisation to your Root project that would automatically generate map files for all o your project code on build time.
3. Adjust package.json to exclude serving all *.map files in ssr_only. This will prevent leaking source map files on client-side
4. Push and deploy your bundle to an MRT env
5. Run npx http-server build --cors to start your local server to host your map files.
   If you server is up correct, you should see some screenshot below
   
6. Start debugging with your MRT site. Open you MRT site as normal. Any error happens there should be loaded with source map in your local server. Sample env with and without source-map connected. https://scaffold-pwa-test-env-2.mobify-storefront.com/

• with source-map
  
• Without source-map
  

Types of Changes

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Documentation update
• Breaking change (could cause existing functionality to not work as expected)
• Other changes (non-breaking changes that does not fit any of the above)

Breaking changes include:

• Removing a public function or component or prop
• Adding a required argument to a function
• Changing the data type of a function parameter or return value
• Adding a new peer dependency to package.json

Changes

How to Test-Drive This PR

• (step1)

Checklists

General

• Changes are covered by test cases
• CHANGELOG.md updated with a short description of changes (not required for documentation updates)

Accessibility Compliance

You must check off all items in one of the follow two lists:

• There are no changes to UI

or...

• Changes were tested with a Screen Reader (iOS VoiceOver or Android Talkback) and had no issues
• Changes comply with WCAG 2.0 guidelines levels A and AA
• Changes to common UI patterns and interactions comply with WAI-ARIA best practices

Localization

• Changes include a UI text update in the Retail React App (which requires translation)

[alexvuong]

This is to tell webpack to expend the sourceMapUrl to a local server that we will run on dev machine.

[alexvuong]

This is important so that MRT does not server source map files to client side