chore(env): SERVER_NAMES variable

- With retro-compatibility with `SERVER_NAME`

Dockerfile

@@ -109,7 +109,7 @@ ENV VPN_SERVICE_PROVIDER=pia \
     # # Nordvpn only:
     SERVER_NUMBER= \
     # # PIA and ProtonVPN only:
-    SERVER_NAME= \
+    SERVER_NAMES= \
     # # ProtonVPN only:
     FREE_ONLY= \
     # # Surfshark only:

internal/configuration/sources/env/serverselection.go

@@ -46,7 +46,8 @@ func (r *Reader) readServerSelection(vpnProvider, vpnType string) (
 	_, hostnamesCSV := r.getEnvWithRetro("SERVER_HOSTNAMES", "SERVER_HOSTNAME")
 	ss.Hostnames = lowerAndSplit(hostnamesCSV)
 
-	ss.Names = envToCSV("SERVER_NAME")
+	_, namesCSV := r.getEnvWithRetro("SERVER_NAMES", "SERVER_NAME")
+	ss.Names = lowerAndSplit(namesCSV)
 
 	if csv := os.Getenv("SERVER_NUMBER"); csv != "" {
 		numbersStrings := strings.Split(csv, ",")