fix(cli)!: protect client Logger and refactor cli scaletest tests (#8317)

- (breaking) Protects Logger and LogBodies fields of codersdk.Client with its mutex. This addresses a data race in cli/scaletest.
- Fillets the existing cli/createworkspaces unit test and moves the testing logic there into the tests under scaletest/createworkspaces.
- Adds testutil.RaceEnabled bool const and conditionaly skips previously-skipped tests under scaletest/ if the race detector is enabled. This is unfortunate and sad, but I would prefer to have these tests at least running without the race detector than not running at all.
- Adds IgnoreErrors option to fake in-memory agent loggers; having the agents fail the test immediately when they encounter any sort of error isn't really helpful.

cli/agent.go

@@ -167,7 +167,7 @@ func (r *RootCmd) workspaceAgent() *clibase.Cmd {
 				slog.F("version", version),
 			)
 			client := agentsdk.New(r.agentURL)
-			client.SDK.Logger = logger
+			client.SDK.SetLogger(logger)
 			// Set a reasonable timeout so requests can't hang forever!
 			// The timeout needs to be reasonably long, because requests
 			// with large payloads can take a bit. e.g. startup scripts