Explore options for automating testing site flow

[taesungh]

Noticed during #446 that there are lots of different possible ways for the login flow to happen with potential edge cases. It would be helpful if we could have a testing mechanism to verify these work as expected. Since many of our site components are async server components, we can consider Setting up Playwright with Next.js for End-to-End testing. One tricky part will be mocking server-side fetch requests to the API as support for this is still experimental. Playwright used to offer an experimental playwright-ssr, but this repository was archived a few months ago. Next.js does offer an Experimental test mode for Playwright which might work for our use cases.

• Install and configure Playwright with Next.js
• Add some test cases for the redirects that happen in different scenarios
  • Provide a helper to mock the user identity provided by /api/user/me
• Include a step in the checks workflow to run the E2E tests
  • Can maybe have the workflow leave a comment on the PR instead of failing a check since this seems experimental for now