Tweak license header scripts (#5649) (#5651)

* Remove newline from license text

* Tweak add license headers script to add newline

Co-authored-by: Steve Gordon <sgordon@hotmail.co.uk>

Author: github-actions[bot]

.github/add-license-headers.sh

@@ -5,7 +5,8 @@ function add_license () {
     (find "$script_path" -name $1 | grep -v "/bin/" | grep -v "/obj/" )|while read fname; do
         line=$(sed -n '2p;3q' "$fname")
         if ! [[ "$line" == " * Licensed to Elasticsearch B.V. under one or more contributor" ]] ; then
-            cat "${script_path}.github/license-header.txt" "$fname" > "${fname}.new"
+            # awk joins the header with the existing file, inserting a newline between them
+            awk '(NR>1 && FNR==1){print ""}1' "${script_path}.github/license-header.txt" "$fname" > "${fname}.new"
             mv "${fname}.new" "$fname"
         fi
     done

.github/license-header.txt

@@ -16,4 +16,3 @@
  * specific language governing permissions and limitations
  * under the License.
  */
-