Cancel Workflows

[thantos]

Should be able to cancel a running workflow execution

1. Fail the workflow with CancelationError
2. cancel all running activities (by the activity looking up the workflow status during heartbeat)
3. Cancel all children workflows that are running
4. make no new commands

await cancelWorkflow(executionId, reason);

// cancels itself (?)
throw new CancelWorkflow(reason);

const execution = workflow.startExecution();
await execution.cancel(reason);

const execution = workflow();
await execution.cancel(reason);

[sam-goodwin]

This seems important lol.

Same with continueAsNew

[thantos]

I think this can be a P1, but it should stay tracked.

[sam-goodwin]

Do we have one for continue as new?