add header linter to avoid license header mistakes (#1414)

Co-authored-by: Daniel Valdivia <18384552+dvaldivia@users.noreply.github.com>

pkg/kes/kes.go

@@ -1,3 +1,19 @@
+// This file is part of MinIO Console Server
+// Copyright (c) 2021 MinIO, Inc.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
 package kes
 
 import (