Maintenance: refactor servers updater code

- Require at least 80% of number of servers now to pass
- Each provider is in its own package with a common structure
- Unzip package with unzipper interface
- Openvpn package with extraction and download functions

internal/updater/providers/cyberghost/servers.go

@@ -0,0 +1,28 @@
+// Package cyberghost contains code to obtain the server information
+// for the Cyberghost provider.
+package cyberghost
+
+import (
+	"context"
+
+	"github.com/qdm12/gluetun/internal/models"
+	"github.com/qdm12/gluetun/internal/updater/resolver"
+)
+
+func GetServers(ctx context.Context, presolver resolver.Parallel,
+	minServers int) (servers []models.CyberghostServer, err error) {
+	possibleServers := getPossibleServers()
+
+	possibleHosts := possibleServers.hostsSlice()
+	hostToIPs, err := resolveHosts(ctx, presolver, possibleHosts, minServers)
+	if err != nil {
+		return nil, err
+	}
+
+	possibleServers.adaptWithIPs(hostToIPs)
+
+	servers = possibleServers.toSlice()
+
+	sortServers(servers)
+	return servers, nil
+}