chore(env): SERVER_REGIONS variable

- With retro-compatibility with `REGION`

Dockerfile

@@ -92,7 +92,7 @@ ENV VPN_SERVICE_PROVIDER=pia \
     WIREGUARD_PUBLIC_KEY= \
     WIREGUARD_ADDRESSES= \
     # VPN server filtering
-    REGION= \
+    SERVER_REGIONS= \
     SERVER_COUNTRIES= \
     SERVER_CITIES= \
     SERVER_HOSTNAME= \

internal/configuration/sources/env/serverselection.go

@@ -35,7 +35,8 @@ func (r *Reader) readServerSelection(vpnProvider, vpnType string) (
 		}
 	}
 
-	ss.Regions = envToCSV("REGION")
+	_, regionsCSV := r.getEnvWithRetro("SERVER_REGIONS", "REGION")
+	ss.Regions = lowerAndSplit(regionsCSV)
 
 	_, citiesCSV := r.getEnvWithRetro("SERVER_CITIES", "CITY")
 	ss.Cities = lowerAndSplit(citiesCSV)

internal/openvpn/logs.go

@@ -54,7 +54,7 @@ That error usually happens because either:
 1. The VPN server IP address you are trying to connect to is no longer valid 🔌
    Update your server information using https://github.com/qdm12/gluetun/wiki/Updating-Servers
 
-2. The VPN server crashed 💥, try changing your VPN servers filtering options such as REGION
+2. The VPN server crashed 💥, try changing your VPN servers filtering options such as SERVER_REGIONS
 
 3. Your Internet connection is not working 🤯, ensure it works