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/resolve.go

@@ -0,0 +1,42 @@
+package cyberghost
+
+import (
+	"context"
+	"net"
+	"time"
+
+	"github.com/qdm12/gluetun/internal/updater/resolver"
+)
+
+func resolveHosts(ctx context.Context, presolver resolver.Parallel,
+	possibleHosts []string, minServers int) (
+	hostToIPs map[string][]net.IP, err error) {
+	const (
+		maxFailRatio    = 1
+		maxDuration     = 10 * time.Second
+		betweenDuration = 500 * time.Millisecond
+		maxNoNew        = 2
+		maxFails        = 10
+	)
+	settings := resolver.ParallelSettings{
+		MaxFailRatio: maxFailRatio,
+		MinFound:     minServers,
+		Repeat: resolver.RepeatSettings{
+			MaxDuration:     maxDuration,
+			BetweenDuration: betweenDuration,
+			MaxNoNew:        maxNoNew,
+			MaxFails:        maxFails,
+			SortIPs:         true,
+		},
+	}
+	hostToIPs, _, err = presolver.Resolve(ctx, possibleHosts, settings)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+
+	return hostToIPs, nil
+}