BUG/MINOR: add missing field when parsing backend balance field

[fabianonunes]

When parsing a backend with the balance option set to uri path-only, the parameter PathOnly is ignored:

func TestBalance(t *testing.T) {
	configFile, _ := os.CreateTemp("/tmp", "")
	_, _ = configFile.WriteString(`
		backend app
		    balance uri path-only
	`)

	config, _ := configuration.New(
		context.Background(),
		options.ConfigurationFile(configFile.Name()),
		options.HAProxyBin("echo"),
		options.TransactionsDir("/tmp"),
	)

	_, backend, _ := config.GetBackend("app", "")
	assert.True(t, backend.Balance.URIPathOnly)
}

[mjuraga]

Thanks for the contribution, LGTM.