Add e2e tests

[kevinwcyu]

E2E testing docs

Add tests for

• Config Editor: Add e2e tests #212
• Query Editor

Tasks

• Remove things referencing cypress, @grafana/e2e, @grafana/e2e-selectors (if they still exist) in package.json, config files, etc.
• Add scripts for playwright:test to run the tests, playwright:report to show the report. Update the github workflow to use playwright:test instead of yarn playwright test and update documentation.
• Add a query editor test without mocking the query endpoint #311

[sarahzinger]

A lot of this was already done by others, but I'll just verify that there's nothing else that needs to be done and close this out.

[sarahzinger]

I'm going to close this ticket for now, since we do have e2e tests for both the query editor and config editor, but there is still one lingering issue that we deprioritized which I've added to the backlog: #311