chore(env): PRIVATE_INTERNET_ACCESS_OPENVPN_ENCRYPTION_PRESET variable

- With retro-compatibility with `PIA_ENCRYPTION` and `ENCRYPTION`

Dockerfile

@@ -100,7 +100,7 @@ ENV VPN_SERVICE_PROVIDER=pia \
     ISP= \
     OWNED_ONLY=no \
     # # Private Internet Access only:
-    PIA_ENCRYPTION= \
+    PRIVATE_INTERNET_ACCESS_OPENVPN_ENCRYPTION_PRESET= \
     PORT_FORWARDING=off \
     PORT_FORWARDING_STATUS_FILE="/tmp/gluetun/forwarded_port" \
     # # Cyberghost only:

internal/configuration/sources/env/openvpn.go

@@ -94,7 +94,9 @@ func readBase64OrNil(envKey string) (valueOrNil *string, err error) {
 }
 
 func (r *Reader) readPIAEncryptionPreset() (presetPtr *string) {
-	_, preset := r.getEnvWithRetro("PIA_ENCRYPTION", "ENCRYPTION")
+	_, preset := r.getEnvWithRetro(
+		"PRIVATE_INTERNET_ACCESS_OPENVPN_ENCRYPTION_PRESET",
+		"PIA_ENCRYPTION", "ENCRYPTION")
 	if preset != "" {
 		return &preset
 	}