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- each vpn provider json data file can contain the `"preferred": true` field to enforce it is used even if outdated, unless there is a version mismatch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

@@ -0,0 +1,68 @@
+package cyberghost
+
+import (
+	"net/netip"
+
+	"github.com/qdm12/gluetun-servers/pkg/constants"
+	"github.com/qdm12/gluetun-servers/pkg/models"
+)
+
+type hostToServer map[string]models.Server
+
+func getPossibleServers() (possibleServers hostToServer) {
+	groupIDToProtocol := getGroupIDToProtocol()
+
+	cyberghostCountryCodes := getSubdomainToRegion()
+	allCountryCodes := constants.CountryCodes()
+	possibleCountryCodes := mergeCountryCodes(cyberghostCountryCodes, allCountryCodes)
+
+	n := len(groupIDToProtocol) * len(possibleCountryCodes)
+
+	possibleServers = make(hostToServer, n) // key is the host
+
+	for groupID, protocol := range groupIDToProtocol {
+		for countryCode, country := range possibleCountryCodes {
+			const domain = "cg-dialup.net"
+			possibleHost := groupID + "-" + countryCode + "." + domain
+			possibleServer := models.Server{
+				VPN:      constants.OpenVPN,
+				Hostname: possibleHost,
+				Country:  country,
+				TCP:      protocol == constants.TCP,
+				UDP:      protocol == constants.UDP,
+			}
+			possibleServers[possibleHost] = possibleServer
+		}
+	}
+
+	return possibleServers
+}
+
+func (hts hostToServer) hostsSlice() (hosts []string) {
+	hosts = make([]string, 0, len(hts))
+	for host := range hts {
+		hosts = append(hosts, host)
+	}
+	return hosts
+}
+
+func (hts hostToServer) adaptWithIPs(hostToIPs map[string][]netip.Addr) {
+	for host, IPs := range hostToIPs {
+		server := hts[host]
+		server.IPs = IPs
+		hts[host] = server
+	}
+	for host, server := range hts {
+		if len(server.IPs) == 0 {
+			delete(hts, host)
+		}
+	}
+}
+
+func (hts hostToServer) toSlice() (servers []models.Server) {
+	servers = make([]models.Server, 0, len(hts))
+	for _, server := range hts {
+		servers = append(servers, server)
+	}
+	return servers
+}