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/purevpn/locationtoserver.go

@@ -0,0 +1,33 @@
+package purevpn
+
+import (
+	"net"
+
+	"github.com/qdm12/gluetun/internal/models"
+)
+
+type locationToServer map[string]models.PurevpnServer
+
+func locationKey(country, region, city string) string {
+	return country + region + city
+}
+
+func (lts locationToServer) add(country, region, city string, ips []net.IP) {
+	key := locationKey(country, region, city)
+	server, ok := lts[key]
+	if !ok {
+		server.Country = country
+		server.Region = region
+		server.City = city
+	}
+	server.IPs = append(server.IPs, ips...)
+	lts[key] = server
+}
+
+func (lts locationToServer) toServersSlice() (servers []models.PurevpnServer) {
+	servers = make([]models.PurevpnServer, 0, len(lts))
+	for _, server := range lts {
+		servers = append(servers, server)
+	}
+	return servers
+}