Add identity to TerminatedFailureInfo + CanceledFailureInfo

[stephanos]

What changed?

Add identity field to TerminatedFailureInfo and CanceledFailureInfo.

Why?

To allow storing the identity of the caller that requested the cancellation/termination; and allow clients to retrieve it.

Breaking changes

No

Server PR

NA - usage example:

&nexusoperationpb.OperationOutcome_Failed{
  Failure: &failurepb.Failure{
    Message: event.Reason,
	FailureInfo: &failurepb.Failure_TerminatedFailureInfo{
	  TerminatedFailureInfo: &failurepb.TerminatedFailureInfo{
        identity: event.Identity,
      },
    },
  },
}

[Quinn-With-Two-Ns]

Does CanceledFailureInfo not need the same field? Like if we need the identity for terminate why not cancel?

[stephanos]

Seems reasonable to me to add it there, too. The only difference AFAICT is that it needs to be threaded through there from the original "cancel" request.

[Quinn-With-Two-Ns]

How is that different then terminate? Isn't it also threaded through?