Add E2E Integration tests to CI

[thedavidprice]

dependent on #1637

Ideally, the CI (via GitHub actions) will do the following:

• Trigger on PR merge (note: also possible to use PR Packages and therefore trigger each PR update, although I'm not sure this is necessary)
• Using the published canary versions, including the canary for create-redwood-app package, run our Cypress test script (here, with files in e2e/ directory). Instructions can be found in Contributing.md
• To figure out --> how to message/notify on success or failure? If this is run outside the PR, where will the alerts show up?

[Tobbe]

• Trigger on PR merge (note: also possible to use PR Packages and therefore trigger each PR update, although I'm not sure this is necessary)

I came here from #1637 to suggest exactly this, but of course you had already thought about it 🙂 I think it's worth it, running on PR updates. Should help ensure we have a stable main branch. Not saying it has been a problem so far, but it will help it stay that way going forward. Would also help with your last point, by blocking merge on failing tests.

[thedavidprice]

We'll just chalk it up to "great minds think alike", right? 😆

Totally game to try on PR updates/commits and see how it works!

[thedavidprice]

Closing in favor of #1886