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- each vpn provider json data file can contain the `"preferred": true` field to enforce it is used even if outdated, unless there is a version mismatch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

@@ -0,0 +1,55 @@
+package hidemyass
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"regexp"
+	"strings"
+)
+
+var indexOpenvpnLinksRegex = regexp.MustCompile(`<a[ ]+href=".+\.ovpn">.+\.ovpn</a>`)
+
+func fetchIndex(ctx context.Context, client *http.Client, indexURL string) (
+	openvpnURLs []string, err error,
+) {
+	request, err := http.NewRequestWithContext(ctx, http.MethodGet, indexURL, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	response, err := client.Do(request)
+	if err != nil {
+		return nil, err
+	}
+	defer response.Body.Close()
+
+	htmlCode, err := io.ReadAll(response.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	if !strings.HasSuffix(indexURL, "/") {
+		indexURL += "/"
+	}
+
+	lines := strings.Split(string(htmlCode), "\n")
+	for _, line := range lines {
+		found := indexOpenvpnLinksRegex.FindString(line)
+		if len(found) == 0 {
+			continue
+		}
+		const prefix = `.ovpn">`
+		const suffix = `</a>`
+		startIndex := strings.Index(found, prefix) + len(prefix)
+		endIndex := strings.Index(found, suffix)
+		filename := found[startIndex:endIndex]
+		openvpnURL := indexURL + filename
+		if !strings.HasSuffix(openvpnURL, ".ovpn") {
+			continue
+		}
+		openvpnURLs = append(openvpnURLs, openvpnURL)
+	}
+
+	return openvpnURLs, nil
+}