Move Demo Store to templates folder

[cartogram]

Fixes Shopify/hydrogen#817

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We noticed that this PR either modifies or introduces usage of the dangerouslySetInnerHTML attribute, which can cause cross-site scripting (XSS) vulnerabilities when user controlled values are passed in.
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[jplhomer]

Thank you!!!

[frandiox]

Thanks!!

With this change, should we also move packages/playground/** to examples? Or even to a different root folder? It doesn't feel like a package 🤔

[cartogram]

@frandiox yeah I agree, playground doesn't feel like it is in the right place.

My thinking here is that we remove that folder entirely and more towards declarative sandboxed e2e apps that are generated before each test runs and destroyed after. The fixture approach won't scale as well and we commonly re-use fixtures across different tests which is not ideal. What do you think? I have a few things started around scaffolding sandbox apps so if you agree with that approach I can put together a PR.