[WIP] DO NOT MERGE - Draft of Updated App Template Example

[DavidWittness]

WHY are these changes introduced?

This is a draft of an updated example for the app tempalte.

The current example of "populate 5 products" is outdated and doesn't provide a good example for something an app developer will build.

WHAT is this pull request doing?

Added 2 new pages:

• Landing page with intro card
• Product tagger page to allow a user to add or remove multiple tags to one or more products

These 2 pages demonstrate the following concepts:

• How to use a Page and Layout
• How to link to an internal page with useNavigate() and a Polaris Link component
• How to organize a page that includes multiple components with shared state
• Calling an internal API from a component
• Loading from the API on user input, showing the loading state
• Passing state objects and functions down to child components
• Uses Polaris components IndexTable, ListBox, ComboBox, and Tag

Added new API functions under /api/producttags

• GET, POST, and DELETE actions
• shows the GraphQL client and how to crate queries with variables
• show how to structure a single file for multiple actions
• shows Promise.all()when multiple API calls need to be made

Existing Issues

• We're stuck in a limbo state while Polaris is doing major updates, do we use Legacy components or Alpha components?
• We're using React 17. It might be nice to update to React 18 to show a demo of Suspense that fetches on a page load (without having to use a useEffect hook)
• The UI for the product tagger is not clear. It probably needs a refactor and an instructions card.

Checklist

Note: once this PR is merged, it becomes a new release for this template.

• [ ] I have added/updated tests for this change
• [ ] I have made changes to the README.md file and other related documentation, if applicable