Fix & feat: Cyberghost server groups

- Allow multiple comma separated values for CYBERGHOST_GROUP
- Defaults to all UDP groups
- If TCP is enabled, defaults to all TCP groups
- Check groups specified match the protocol
- Default Cyberghost group to empty
- Adjust formatting and messages

internal/constants/cyberghost_test.go

@@ -0,0 +1,18 @@
+package constants
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_CyberghostGroupChoices(t *testing.T) {
+	t.Parallel()
+
+	expected := []string{"Premium TCP Asia", "Premium TCP Europe",
+		"Premium TCP USA", "Premium UDP Asia", "Premium UDP Europe",
+		"Premium UDP USA"}
+	choices := CyberghostGroupChoices()
+
+	assert.Equal(t, expected, choices)
+}