Feat: rework Surfshark servers data (#575)

- Feat: `MULTIHOP_ONLY` variable
- Feat: `COUNTRY` variable
- Feat: `CITY` variable
- Feat: `REGION` variable, with retro-compatibility
- Feat: merge servers from API, zip and hardcoded hostnames
- Fix: remove outdated and duplicate servers
- Maint: faster update with fully parallel DNS resolutions

internal/updater/providers/surfshark/location.go

@@ -0,0 +1,22 @@
+package surfshark
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/qdm12/gluetun/internal/models"
+)
+
+var (
+	errHostnameNotFound = errors.New("hostname not found in hostname to location mapping")
+)
+
+func getHostInformation(host string, hostnameToLocation map[string]models.SurfsharkLocationData) (
+	data models.SurfsharkLocationData, err error) {
+	locationData, ok := hostnameToLocation[host]
+	if !ok {
+		return locationData, fmt.Errorf("%w: %s", errHostnameNotFound, host)
+	}
+
+	return locationData, nil
+}