Functionality to pause flows has already been added, but only hospitalised flows were able to be paused (as they were not actually running).
We now need the ability to pause running flows.
This can be done by updating the status of all `RUNNING` flows in the in-memory flow cache (`HOSPITALIZED` has already been done). When reaching the next suspend action, the state machine should check whether the checkpoint is not `PAUSED`. If it is not, then it continues running as normal, otherwise, it should stop processing.