Add very basic E2E test using cypress

[rbren]

Summary We should have an e2e test that loads OD in the browser and runs it through a basic interaction to make sure it works.

Motivation We recently tripped over a bug in the server which wasn't tested: https://github.com/OpenDevin/OpenDevin/issues/1782

Technical Design Probably using cypress?

We should use the DummyAgent, which doesn't need an LLM--it just cycles through a few common actions (reading, writing, running commands, etc)