added cassandra port binding localhost:9042

In order to _local_ develop astarte via `dev mode`, using [`astarte-dev-tool up`](astarte-platform#978)  or using `docker compose watch`, cassandra/scylla needs to expose the port used to connection. Otherwise, the connection are only available via cluster.

With this PR scylla/cassandra is exposed on `localhost:9042`

Signed-off-by: Gabriele Ghio <gabriele.ghio@secomind.com>

docker-compose.dev.yml

@@ -114,3 +114,6 @@ services:
       watch:
         - path: apps/astarte_trigger_engine/lib
           action: rebuild
+  scylla:
+    ports:
+      - "9042:9042"