feat(storage): storage file structure changes (#3301)

- migrate persisted server data storage from `/gluetun/servers.json` to `/gluetun/servers/`
- add `STORAGE_SERVERS_ENABLED=on` to enable or disable on-disk server data storage
- add `STORAGE_SERVERS_DIRECTORY_PATH=/gluetun/servers` to configure where per-provider server files are stored
- keep backward compatibility with legacy `STORAGE_FILEPATH=/gluetun/servers.json`
- automatically read and migrate legacy `/gluetun/servers.json` into the new `/gluetun/servers/` layout when needed
- try to remove the legacy servers file after a successful migration to the new storage directory
- switch persisted server data from one large JSON file to a manifest plus per-provider JSON files
- add `UPDATER_PREFER_DIRECT_DOWNLOAD` to allow preferring direct download of provider server data
- keep deprecated updater flags `-enduser` and `-maintainer` as no-op warnings for backward compatibility
- preserve compatibility checks so persisted server data is discarded when its schema version no longer matches the built-in data
- allow preferred persisted provider data to override built-in data when versions match
- servers data now lives at https://github.com/qdm12/gluetun-servers/tree/main/pkg/servers

internal/cli/openvpnconfig.go

@@ -9,12 +9,10 @@ import (
 	"time"
 
 	"github.com/qdm12/gluetun/internal/configuration/settings"
-	"github.com/qdm12/gluetun/internal/constants"
 	"github.com/qdm12/gluetun/internal/models"
 	"github.com/qdm12/gluetun/internal/netlink"
 	"github.com/qdm12/gluetun/internal/openvpn/extract"
 	"github.com/qdm12/gluetun/internal/provider"
-	"github.com/qdm12/gluetun/internal/storage"
 	"github.com/qdm12/gluetun/internal/updater/resolver"
 	"github.com/qdm12/gosettings/reader"
 )
@@ -49,9 +47,9 @@ type IPv6Checker interface {
 func (c *CLI) OpenvpnConfig(logger OpenvpnConfigLogger, reader *reader.Reader,
 	ipv6Checker IPv6Checker,
 ) error {
-	storage, err := storage.New(logger, constants.ServersData)
+	storage, err := setupStorage(newNoopLogger())
 	if err != nil {
-		return err
+		return fmt.Errorf("setting up storage: %w", err)
 	}
 
 	var allSettings settings.Settings