Maint: split custom config files in openvpn/custom

internal/openvpn/custom/helpers_test.go

@@ -0,0 +1,14 @@
+package custom
+
+import (
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func removeFile(t *testing.T, filename string) {
+	t.Helper()
+	err := os.RemoveAll(filename)
+	require.NoError(t, err)
+}