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- each vpn provider json data file can contain the `"preferred": true` field to enforce it is used even if outdated, unless there is a version mismatch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

@@ -0,0 +1,38 @@
+package ipvanish
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/qdm12/gluetun-servers/pkg/constants"
+	"golang.org/x/text/cases"
+)
+
+func parseFilename(fileName, hostname string, titleCaser cases.Caser) (
+	country, city string, err error,
+) {
+	const prefix = "ipvanish-"
+	s := strings.TrimPrefix(fileName, prefix)
+
+	const ext = ".ovpn"
+	host := strings.Split(hostname, ".")[0]
+	suffix := "-" + host + ext
+	s = strings.TrimSuffix(s, suffix)
+
+	parts := strings.Split(s, "-")
+
+	countryCodes := constants.CountryCodes()
+	countryCode := strings.ToLower(parts[0])
+	country, ok := countryCodes[countryCode]
+	if !ok {
+		return "", "", fmt.Errorf("country code is unknown: %s", countryCode)
+	}
+	country = titleCaser.String(country)
+
+	if len(parts) > 1 {
+		city = strings.Join(parts[1:], " ")
+		city = titleCaser.String(city)
+	}
+
+	return country, city, nil
+}