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/privado/hosttoserver.go

@@ -0,0 +1,53 @@
+package privado
+
+import (
+	"net"
+
+	"github.com/qdm12/gluetun/internal/models"
+)
+
+type hostToServer map[string]models.PrivadoServer
+
+func (hts hostToServer) add(host string) {
+	server, ok := hts[host]
+	if ok {
+		return
+	}
+	server.Hostname = host
+	hts[host] = server
+}
+
+func (hts hostToServer) toHostsSlice() (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][]net.IP) (
+	warnings []string) {
+	for host, IPs := range hostToIPs {
+		if len(IPs) > 1 {
+			warning := "more than one IP address found for host " + host
+			warnings = append(warnings, warning)
+		}
+		server := hts[host]
+		server.IP = IPs[0]
+		hts[host] = server
+	}
+	for host, server := range hts {
+		if server.IP == nil {
+			delete(hts, host)
+		}
+	}
+	return warnings
+}
+
+func (hts hostToServer) toServersSlice() (servers []models.PrivadoServer) {
+	servers = make([]models.PrivadoServer, 0, len(hts))
+	for _, server := range hts {
+		servers = append(servers, server)
+	}
+	return servers
+}