deployment: add volume for graphdb storage

deployment/docker-compose.yml

@@ -8,6 +8,8 @@ services:
                 image: "khaller/graphdb-free:1.2.2-graphdb9.1.1"
                 ports:
                         - ${ULOCOMPOSE_DBPORT}:7200
+                volumes:
+                        - graphdb-volume:/opt/graphdb/data
 
         ulocollectweb:
                 image: "schaertl/ulocollectweb"
@@ -21,3 +23,6 @@ services:
                         - ULOAPPS_REMOTE_REPOSITORY=compose
                 ports:
                         - ${ULOCOMPOSE_APPPORT}:7400
+
+volumes:
+        graphdb-volume: