chore(updater): incorporate FetchServers method in Provider interface

- Each provider interface can now fetch updated servers data
- Rename each provider updater subpackage name to `updater`
- Updater constructor does not take a settings struct
- Updater update method takes in a slice of provider strings

internal/provider/protonvpn/provider.go

@@ -2,9 +2,11 @@ package protonvpn
 
 import (
 	"math/rand"
+	"net/http"
 
 	"github.com/qdm12/gluetun/internal/constants/providers"
 	"github.com/qdm12/gluetun/internal/provider/common"
+	"github.com/qdm12/gluetun/internal/provider/protonvpn/updater"
 	"github.com/qdm12/gluetun/internal/provider/utils"
 )
 
@@ -12,13 +14,16 @@ type Provider struct {
 	storage    common.Storage
 	randSource rand.Source
 	utils.NoPortForwarder
+	common.Fetcher
 }
 
-func New(storage common.Storage, randSource rand.Source) *Provider {
+func New(storage common.Storage, randSource rand.Source,
+	client *http.Client, updaterWarner common.Warner) *Provider {
 	return &Provider{
 		storage:         storage,
 		randSource:      randSource,
 		NoPortForwarder: utils.NewNoPortForwarding(providers.Protonvpn),
+		Fetcher:         updater.New(client, updaterWarner),
 	}
 }