Allow `202` Accepted response on cancel task

[markjschreiber]

The cancellation of a task might not be synchronous, in some implementations it might be a multi-step operation or a notification sent to a event bus or pub sub queue, and for fast running tasks it may not be processed before the task is complete.

From the RFC

10.2.3 202 Accepted

The request has been accepted for processing, but the processing has not been completed. The request might or might not eventually be acted upon, as it might be disallowed when processing actually takes place. There is no facility for re-sending a status code from an asynchronous operation such as this.

The 202 response is intentionally non-committal. Its purpose is to allow a server to accept a request for some other process (perhaps a batch-oriented process that is only run once per day) without requiring that the user agent's connection to the server persist until the process is completed. The entity returned with this response SHOULD include an indication of the request's current status and either a pointer to a status monitor or some estimate of when the user can expect the request to be fulfilled.

Given that, a 202 response might be more appropriate.

[uniqueg]

This was perhaps addressed by returning CANCELLING instead of CANCELLED?