Add e2e UI tests

[markphelps]

Is your feature request related to a problem? Please describe.
Add some end to end UI tests to verify that changes do not break the Flipt UI and that users see the expected results.

Describe the solution you'd like
Perhaps something like testcafe? I dont know much about the 'modern' e2e Javascript testing frameworks.. but I know things I DO NOT WANT:

❌ No ❌ :

• Selenium or browser based tests as these are slow and error prone
• BDD testing language, just want simple easy to write expectation based tests

Additional context
Something that could capture screenshots when tests fail would be nice too for local development

[jperl]

👋 Hello I maintain an open source library that generates Playwright code. I would be happy to submit PRs setting up e2e tests, if you are cool with them using Playwright?

[markphelps]

@jperl Yes that would be awesome! This is the first I've heard of Playwright, but it looks great, as does QAWolf (love your landing page btw).

[jperl]

Thank you :). Awesome, I will start working on a PR next week!