gitlab-ci: Check merge requests for Signed-off-by trailers

Based on Andreas work in

https://gitlab.com/libssh/libssh-mirror/-/merge_requests/104/

Signed-off-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

.gitlab-ci/git-check-signoff-trailer.sh

@@ -0,0 +1,36 @@
+#!/bin/bash
+
+if [ $# != 1 ]; then
+    echo "Usage: $0 UPSTREAM_COMMIT_SHA"
+    exit 1
+fi
+
+failed=0
+
+if [ -z "$CI_COMMIT_SHA" ]; then
+    echo "CI_COMMIT_SHA is not set"
+    exit 1
+fi
+
+CI_COMMIT_RANGE="$1..$CI_COMMIT_SHA"
+
+red='\033[0;31m'
+blue='\033[0;34m'
+
+echo -e "${blue}Checking commit range: $CI_COMMIT_RANGE"
+echo
+echo
+
+for commit in `git rev-list $CI_COMMIT_RANGE`; do
+    git show -s --format=%B $commit | grep "^Signed-off-by: " 2>&1 >/dev/null
+    ret=$?
+    if [ $ret -eq 1 ]; then
+        echo -e "${red}  >>> Missing Signed-off-by trailer in commit $commit"
+        failed=`expr $failed + 1`
+    fi
+done
+
+echo
+echo
+
+exit $failed