[CHORE] Add playwright eslint plugin

- Add https://github.com/playwright-community/eslint-plugin-playwright
as a linter for the playwright tests.
- `no-networkidle` and `no-conditional-in-test` are disabled as fixing
those doesn't seem to really improve testing quality for our use case.
- Some non-recommended linters are enabled to ensure consistency (the
prefer rules).

tests/e2e/explore.test.e2e.js

@@ -1,6 +1,6 @@
 // @ts-check
 // document is a global in evaluate, so it's safe to ignore here
-/* eslint no-undef: 0 */
+// eslint playwright/no-conditional-in-test: 0
 import {test, expect} from '@playwright/test';
 
 test('Explore view taborder', async ({page}) => {