Maintenance: refactor servers updater code

- Require at least 80% of number of servers now to pass
- Each provider is in its own package with a common structure
- Unzip package with unzipper interface
- Openvpn package with extraction and download functions

internal/updater/providers/cyberghost/countries.go

@@ -0,0 +1,15 @@
+package cyberghost
+
+func mergeCountryCodes(base, extend map[string]string) (merged map[string]string) {
+	merged = make(map[string]string, len(base))
+	for countryCode, region := range base {
+		merged[countryCode] = region
+	}
+	for countryCode := range base {
+		delete(extend, countryCode)
+	}
+	for countryCode, region := range extend {
+		merged[countryCode] = region
+	}
+	return merged
+}