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- each vpn provider json data file can contain the `"preferred": true` field to enforce it is used even if outdated, unless there is a version mismatch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

@@ -0,0 +1,65 @@
+package windscribe
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/netip"
+	"strconv"
+	"time"
+)
+
+type apiData struct {
+	Data []regionData `json:"data"`
+}
+
+type regionData struct {
+	Region string      `json:"name"`
+	Groups []groupData `json:"groups"`
+}
+
+type groupData struct {
+	City     string       `json:"city"`
+	Nodes    []serverData `json:"nodes"`
+	OvpnX509 string       `json:"ovpn_x509"`
+	WgPubKey string       `json:"wg_pubkey"`
+}
+
+type serverData struct {
+	Hostname string     `json:"hostname"`
+	IP       netip.Addr `json:"ip"`
+	IP2      netip.Addr `json:"ip2"`
+	IP3      netip.Addr `json:"ip3"`
+}
+
+func fetchAPI(ctx context.Context, client *http.Client) (
+	data apiData, err error,
+) {
+	const baseURL = "https://assets.windscribe.com/serverlist/mob-v2/1/"
+	cacheBreaker := time.Now().Unix()
+	url := baseURL + strconv.Itoa(int(cacheBreaker))
+
+	request, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+	if err != nil {
+		return data, err
+	}
+
+	response, err := client.Do(request)
+	if err != nil {
+		return data, err
+	}
+	defer response.Body.Close()
+
+	if response.StatusCode != http.StatusOK {
+		return data, fmt.Errorf("HTTP status code not OK: %d %s",
+			response.StatusCode, response.Status)
+	}
+
+	decoder := json.NewDecoder(response.Body)
+	if err := decoder.Decode(&data); err != nil {
+		return data, fmt.Errorf("decoding response body: %w", err)
+	}
+
+	return data, nil
+}