New PIA servers support (#227)

* Adapt storage: SyncServers write to file option, export FlushToFile
* CLI built-in updater for old and new PIA servers
* Update hardcoded IP addresses for PIA old and new servers
* Add PIA old to allServers struct and update timestamps
* Adapt code to work with new and old PIA servers
* Remove PIA subdomains (unneeded) from resolver tool

internal/updater/pia.go

@@ -0,0 +1,66 @@
+package updater
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+
+	"github.com/qdm12/gluetun/internal/models"
+)
+
+func findPIAServers(new bool) (servers []models.PIAServer, err error) {
+	zipURL := "https://www.privateinternetaccess.com/openvpn/openvpn-ip.zip"
+	if new {
+		zipURL = "https://www.privateinternetaccess.com/openvpn/openvpn-ip-nextgen.zip"
+	}
+	return findPIAServersFromURL(zipURL)
+}
+
+func findPIAServersFromURL(zipURL string) (servers []models.PIAServer, err error) {
+	contents, err := fetchAndExtractFiles(zipURL)
+	if err != nil {
+		return nil, err
+	}
+	for fileName, content := range contents {
+		remoteLines := extractRemoteLinesFromOpenvpn(content)
+		if len(remoteLines) == 0 {
+			return nil, fmt.Errorf("cannot find any remote lines in %s", fileName)
+		}
+		IPs := extractIPsFromRemoteLines(remoteLines)
+		if len(IPs) == 0 {
+			return nil, fmt.Errorf("cannot find any IP addresses in %s", fileName)
+		}
+		region := strings.TrimSuffix(fileName, ".ovpn")
+		server := models.PIAServer{
+			Region: region,
+			IPs:    IPs,
+		}
+		servers = append(servers, server)
+	}
+	sort.Slice(servers, func(i, j int) bool {
+		return servers[i].Region < servers[j].Region
+	})
+	return servers, nil
+}
+
+func stringifyPIAServers(servers []models.PIAServer) (s string) {
+	s = "func PIAServers() []models.PIAServer {\n"
+	s += "	return []models.PIAServer{\n"
+	for _, server := range servers {
+		s += "		" + server.String() + ",\n"
+	}
+	s += "	}\n"
+	s += "}"
+	return s
+}
+
+func stringifyPIAOldServers(servers []models.PIAServer) (s string) {
+	s = "func PIAOldServers() []models.PIAServer {\n"
+	s += "	return []models.PIAServer{\n"
+	for _, server := range servers {
+		s += "		" + server.String() + ",\n"
+	}
+	s += "	}\n"
+	s += "}"
+	return s
+}