UI sanity testing in e2e

[prestonvanloon]

🚀 Feature Request

Description

Prysm UI has suffered from multiple critical issues in new releases such as the UI not serving at all, CORS issues, etc.

I started some work in #8981, but it turned stale and will need to be reworked.

Describe the solution you'd like

• Add selenium based e2e testing for the UI.
• Update CI runners to have a headless chrome browser
• Add more testing of the basic user flow to ensure the most critical functionality works as expected

Describe alternatives you've considered

None.

[james-prysm]

https://prysmaticlabs.notion.site/UI-Integration-Testing-212a3d948ebb47c68cda196ea6be5509
will be updating strategy here for what kind of tests we can start and other considerations

[prestonvanloon]

Progress resumed in #9782.

One blocker is that our continuous integration system needs to add support for headless browser tests. The idea we have is to use external webdriver runners that the build agents could use to run the UI tests.

[prestonvanloon]

External webdriver could be an instance of selenium/standalone-chrome docker image or selenium grid.

[prestonvanloon]

Perhaps bazel can spin up the standalone docker image. That would be something interesting to add and reduce infrastructure requirements.

[james-prysm]

Probably isn't needed anymore for this, unless we figure out what we want to do with web ui going forward.