Adding ability to run user level pre-commit hooks (#11923)

* Adding ability to run user level pre-commit hooks
* Adding pre-commit docs in CONTRIBUTING.md

pre-commit.sh

@@ -6,3 +6,22 @@ if [ -z $AWX_IGNORE_BLACK ] ; then
         	exit 1)
 	fi
 fi
+
+if [ -z $AWX_IGNORE_USER ] ; then
+	FAIL=0
+	export CHANGED_FILES=$(git diff --cached --name-only --diff-filter=AM)
+	if [ -d ./pre-commit-user ] ; then
+		for SCRIPT in `find ./pre-commit-user -executable -type f` ; do
+			echo "Running user pre-commit hook $SCRIPT"
+			$SCRIPT
+			if [ $? != 0 ] ; then
+				echo "User test $SCRIPT failed"
+			       	FAIL=1
+			fi
+		done
+	fi
+	if [ $FAIL == 1 ] ; then
+		echo "One or more user tests failed, see messages above"
+		exit 1
+	fi
+fi