Replace interrupting sessions by flow by ignoring waiting sessions with no flow

[rowanseymour]

Currently when you archive a flow, it triggers a task to interrupt all the waiting sessions associated with that flow. There are two problems with this:

• It's potentially very expensive as there could be millions of waiting sessions. What if the user archived the flow my mistake?
• It requires having all sessions retrievable by flow - and we're trying to limit the access the patterns for sessions with the end goal of storing them outside of postgres.