Add POS UI Extensions tutorial code examples

[kangjoa]

Partially resolves issue #21021

Description

Migrates remaining tutorial code from ui-extensions to this centralized tutorial repo (see issue for more details). The coordinating tutorials will be updated in the dev docs to use these new links.

What's included

• example-pos-ui-extensions--discounts--preact: Discount extension tutorial
• example-pos-ui-extensions--printer--preact: Printer extension with full app setup
• example-pos-ui-extensions--localize--preact: removes values for client_id and author

Tophat

• Copy the tutorial code, install dependencies with npm install, start development with shopify app dev and follow CLI prompts to reset. Apps will be runnable.

[vctrchu]

This is a good start but I think we should keep the examples as clean as we can by minimizing what we commit.

Could you try mirroring the customer-accounts examples?

[kangjoa]

I kept the Docker and config files based on the other app tutorials, including the Build a Shopify app using React Router tutorial

[vctrchu]

I tried testing the print extension tutorial by just copy pasting all the files but ran into some blockers which require the developer to actually initialize their own app first. I'm not sure how much value we get from committing all the template files from the react router template.

How about instead, we only commit the extensions folder & the app folder since those are crucial for the tutorial?

UPDATE: we will use only update the client id for each app toml file but keep everything that is generated from the templates to make running the extension easy for developers.

[vctrchu]

~~ We should update the READ on instructions on how to run each app ~~
~~- cd the app you want to run ~~
~~- shopify app dev --reset ~~

We talked and agreed there is already sufficient documentation in each example READ ME + CLI warnings.

[vctrchu]

Looks great!