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- each vpn provider json data file can contain the `"preferred": true` field to enforce it is used even if outdated, unless there is a version mismatch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/torguard/filename.go

@@ -0,0 +1,35 @@
+package torguard
+
+import (
+	"strings"
+
+	"golang.org/x/text/cases"
+)
+
+func parseFilename(fileName string, titleCaser cases.Caser) (country, city string) {
+	const prefix = "TorGuard."
+	const suffix = ".ovpn"
+	s := strings.TrimPrefix(fileName, prefix)
+	s = strings.TrimSuffix(s, suffix)
+
+	switch {
+	case strings.Count(s, ".") == 1 && !strings.HasPrefix(s, "USA"):
+		parts := strings.Split(s, ".")
+		country = parts[0]
+		city = parts[1]
+
+	case strings.HasPrefix(s, "USA"):
+		country = "USA"
+		s = strings.TrimPrefix(s, "USA-")
+		s = strings.ReplaceAll(s, "-", " ")
+		s = strings.ReplaceAll(s, ".", " ")
+		s = strings.ToLower(s)
+		s = titleCaser.String(s)
+		city = s
+
+	default:
+		country = s
+	}
+
+	return country, city
+}