feat: Initial E2E test framework for v2 (#288)

This brings an initial E2E test (really, an integration test - it's only running the server locally, as opposed to against a deployment - but it'd be easy to point playwright to a deployment).

Demo gif:
![test2](https://user-images.githubusercontent.com/88213859/156078517-6cb4ef84-337b-4e16-a8bc-aea7d06dcbcb.gif)

This test exercises a minimal flow for login:
- Run the `coderd` binary to start a server on 3000
- Create an initial user as part of setup
- Go through the login flow and verify we land on the projects page

It will be useful to have to ensure that #360 doesn't introduce a regression in the login flow

Future E2E tests that would be useful:
- Create a project & verify it shows in the UI
- Create a workspace and verify it shows in the UI

scripts/datadog-cireport/main.go

@@ -75,7 +75,8 @@ func main() {
 		"service":              "coder",
 		"_dd.cireport_version": "2",
 
-		"test.traits": fmt.Sprintf(`{"database":["%s"]}`, os.Getenv("DD_DATABASE")),
+		"test.traits": fmt.Sprintf(`{"database":["%s"], "category":["%s"]}`,
+			os.Getenv("DD_DATABASE"), os.Getenv("DD_CATEGORY")),
 
 		// Additional tags found in DataDog docs. See:
 		// https://docs.datadoghq.com/continuous_integration/setup_tests/junit_upload/#collecting-environment-configuration-metadata