[copyright] add MIT license headers to .sh scripts where missing

Years are set according to 'git log' history

Github-Pull: #8700
Rebased-From: 0766d1cac38d7ea27a6323d7ca206154b2686f9b

contrib/devtools/git-subtree-check.sh

@@ -1,4 +1,7 @@
 #!/bin/sh
+# Copyright (c) 2015 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 DIR="$1"
 COMMIT="$2"