refactor(storage): new storage file structure

- new directory structure containing manifest.json and one json file per provider, by default.
- the manifest.json file can specify a filepath for each vpn provider
- each vpn provider json data file can contain the `"preferred": true` field to enforce it is used even if outdated, unless there is a version mismatch
- `STORAGE_SERVERS_DIRECTORY_PATH` replaces `STORAGE_FILEPATH` (which is now a migration source only). It sets the directory where server manifest and per-provider JSON files are stored (default: `/gluetun/servers/`).
- First-run migration: On startup, gluetun checks for the old /gluetun/servers.json file; if found and no new manifest exists, it automatically migrates all data to /gluetun/servers/ directory structure
- Silent fallback: If legacy file isn't found, uses the new directory path normally
- Legacy cleanup: After successful migration, attempts to remove the old fat JSON file (logs warning only if removal fails, e.g., read-only bind mounts)

gluetun-servers/pkg/updaters/providers/privatevpn/filename.go

@@ -0,0 +1,48 @@
+package privatevpn
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+)
+
+var trailingNumber = regexp.MustCompile(` [0-9]+$`)
+
+func parseFilename(fileName string) (
+	countryCode, city string, err error,
+) {
+	fileName = strings.ReplaceAll(fileName, " ", "") // remove spaces
+
+	const prefix = "PrivateVPN-"
+	if !strings.HasPrefix(fileName, prefix) {
+		return "", "", fmt.Errorf("bad prefix in file name %s", fileName)
+	}
+	s := strings.TrimPrefix(fileName, prefix)
+
+	const tcpSuffix = "-TUN-443.ovpn"
+	const udpSuffix = "-TUN-1194.ovpn"
+	switch {
+	case strings.HasSuffix(fileName, tcpSuffix):
+		s = strings.TrimSuffix(s, tcpSuffix)
+	case strings.HasSuffix(fileName, udpSuffix):
+		s = strings.TrimSuffix(s, udpSuffix)
+	default:
+		return "", "", fmt.Errorf("bad suffix in file name %s", fileName)
+	}
+
+	s = trailingNumber.ReplaceAllString(s, "")
+
+	parts := strings.Split(s, "-")
+	const minParts = 2
+	if len(parts) < minParts {
+		return "", "", fmt.Errorf("not enough parts in file name %s", fileName)
+	}
+	countryCode, city = parts[0], parts[1]
+
+	countryCode = strings.ToLower(countryCode)
+	if countryCode == "co" && strings.HasPrefix(city, "Bogot") {
+		city = "Bogota"
+	}
+
+	return countryCode, city, nil
+}