Shut down websocket connections when subgraphs are stopped

[Jannis]

Follow-up based on the discussion here: #640 (comment).

[timmclean]

This sounds tricky because of the separation between query and index nodes. How about subscribing to SubgraphStateEntity deletions and acting on those? (assuming I get the multiple version PR through code review)

[fordN]

This issue is old and Websockets aren't even supported anymore , closing.