feat(pia): port forwarding options VPN_PORT_FORWARDING_USERNAME and VPN_PORT_FORWARDING_PASSWORD

- Retro-compatible with `OPENVPN_USER` + `OPENVPN_PASSWORD`
- No more reading for the OpenVPN auth file
- Allow to use PIA port forwarding with Wireguard

internal/provider/privateinternetaccess/provider.go

@@ -5,7 +5,6 @@ import (
 	"net/http"
 	"time"
 
-	"github.com/qdm12/gluetun/internal/constants/openvpn"
 	"github.com/qdm12/gluetun/internal/constants/providers"
 	"github.com/qdm12/gluetun/internal/provider/common"
 	"github.com/qdm12/gluetun/internal/provider/privateinternetaccess/updater"
@@ -18,7 +17,6 @@ type Provider struct {
 	common.Fetcher
 	// Port forwarding
 	portForwardPath string
-	authFilePath    string
 }
 
 func New(storage common.Storage, randSource rand.Source,
@@ -29,7 +27,6 @@ func New(storage common.Storage, randSource rand.Source,
 		timeNow:         timeNow,
 		randSource:      randSource,
 		portForwardPath: jsonPortForwardPath,
-		authFilePath:    openvpn.AuthConf,
 		Fetcher:         updater.New(client),
 	}
 }