chore(surfshark): add package internal/provider/surshark/server

- Merge `internal/models/location.go` and `internal/constants/surfshark.go` into `internal/provider/surfshark/servers/locationdata.go`

internal/configuration/settings/validation/surfshark.go

@@ -1,12 +1,12 @@
 package validation
 
 import (
-	"github.com/qdm12/gluetun/internal/constants"
+	"github.com/qdm12/gluetun/internal/provider/surfshark/servers"
 )
 
 // TODO remove in v4.
 func SurfsharkRetroLocChoices() (choices []string) {
-	locationData := constants.SurfsharkLocationData()
+	locationData := servers.LocationData()
 	choices = make([]string, 0, len(locationData))
 	seen := make(map[string]struct{}, len(locationData))
 	for _, data := range locationData {