move users service to app directory (#18257)

app/session.go

@@ -10,9 +10,9 @@ import (
 	"net/http"
 	"os"
 
+	"github.com/mattermost/mattermost-server/v6/app/users"
 	"github.com/mattermost/mattermost-server/v6/audit"
 	"github.com/mattermost/mattermost-server/v6/model"
-	"github.com/mattermost/mattermost-server/v6/services/users"
 	"github.com/mattermost/mattermost-server/v6/shared/mlog"
 	"github.com/mattermost/mattermost-server/v6/store"
 )