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/configuration/provider_test.go

@@ -24,7 +24,7 @@ func Test_Provider_lines(t *testing.T) {
 			settings: Provider{
 				Name: constants.Cyberghost,
 				ServerSelection: ServerSelection{
-					Group:   "group",
+					Groups:  []string{"group"},
 					Regions: []string{"a", "El country"},
 				},
 				ExtraConfigOptions: ExtraConfigOptions{
@@ -35,7 +35,7 @@ func Test_Provider_lines(t *testing.T) {
 			lines: []string{
 				"|--Cyberghost settings:",
 				"   |--Network protocol: udp",
-				"   |--Server group: group",
+				"   |--Server groups: group",
 				"   |--Regions: a, El country",
 				"   |--Client key is set",
 				"   |--Client certificate is set",