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/surfshark/sort.go

@@ -0,0 +1,13 @@
+package surfshark
+
+import (
+	"sort"
+
+	"github.com/qdm12/gluetun/internal/models"
+)
+
+func sortServers(servers []models.SurfsharkServer) {
+	sort.Slice(servers, func(i, j int) bool {
+		return servers[i].Region < servers[j].Region
+	})
+}