chore: move cypress out of demo and fix set up

[tiffafoo]

Summary

• Move cypress out of demo
• Add ci specific config and dev specific config
• Fix testing-library types not being found

This PR is the base in which all the tests are written on top of so should be merged first.

Test plan

1. Visit the Deploy Preview Logs: https://app.netlify.com/sites/netlify-plugin-nextjs-demo/deploys/6184066e70c9010007ed5ccf#L379
2. See that cypress runs the testing-library test correctly

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1. Checkout this branch
2. Run npm run cy:open
3. In the GUI that pens, run the test
4. See that it runs the test and everything passes

Relevant links (GitHub issues, Notion docs, etc.) or a picture of cute animal (small picture)

https://github.com/netlify/pod-ecosystem-integrations/issues/33

Standard checks:

• Check the Deploy Preview's Demo site for your PR's functionality
• Add docs when necessary

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🧪 Once merged, make sure to update the version if needed and that it was published correctly.

[ascorbic]

Great!