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/cyberghost/updater/constants.go

@@ -1,4 +1,4 @@
-package cyberghost
+package updater
 
 import "github.com/qdm12/gluetun/internal/constants"
 

internal/provider/cyberghost/updater/countries.go

@@ -1,4 +1,4 @@
-package cyberghost
+package updater
 
 func mergeCountryCodes(base, extend map[string]string) (merged map[string]string) {
 	merged = make(map[string]string, len(base))

internal/provider/cyberghost/updater/hosttoserver.go

@@ -1,4 +1,4 @@
-package cyberghost
+package updater
 
 import (
 	"net"

internal/provider/cyberghost/updater/resolve.go

@@ -1,4 +1,4 @@
-package cyberghost
+package updater
 
 import (
 	"time"

internal/provider/cyberghost/updater/servers.go

@@ -1,6 +1,6 @@
-// Package cyberghost contains code to obtain the server information
+// Package updater contains code to obtain the server information
 // for the Cyberghost provider.
-package cyberghost
+package updater
 
 import (
 	"context"

internal/provider/cyberghost/updater/updater.go

@@ -1,4 +1,4 @@
-package cyberghost
+package updater
 
 import (
 	"github.com/qdm12/gluetun/internal/provider/common"