marker: fix PUT marker with an enabled-only body (bpf no longer required)

update_marker reused MarkerCreate, whose bpf is required, so a partial PUT like
{"enabled": false} was rejected with 422 "bpf field required". Add a MarkerUpdate
schema with every field optional (bpf included; capture_node_id and name are
create-only/path-driven and omitted) and use it for the PUT route — partial
updates now validate cleanly.

gns3server/api/routes/controller/links.py

@@ -497,7 +497,7 @@ async def delete_marker(
 )
 async def update_marker(
     marker_name: str,
-    marker_data: schemas.MarkerCreate,
+    marker_data: schemas.MarkerUpdate,
     link: Link = Depends(dep_link)
 ) -> dict:
     """