Add identity to TerminatedFailureInfo + CanceledFailureInfo (#745)

<!-- Describe what has changed in this PR -->
**What changed?**

Add `identity` field to `TerminatedFailureInfo` and
`CanceledFailureInfo`.

<!-- Tell your future self why have you made these changes -->
**Why?**

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

<!-- Are there any breaking changes on binary or code level? -->
**Breaking changes**

No

<!-- If this breaks the Server, please provide the Server PR to merge
right after this PR was merged. -->
**Server PR**

NA - usage example:

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

Author: stephanos

openapi/openapiv2.json

@@ -12162,6 +12162,10 @@
       "properties": {
         "details": {
           "$ref": "#/definitions/v1Payloads"
+        },
+        "identity": {
+          "type": "string",
+          "description": "The identity of the worker or client that requested the cancellation."
         }
       }
     },
@@ -16887,7 +16891,13 @@
       "type": "object"
     },
     "v1TerminatedFailureInfo": {
-      "type": "object"
+      "type": "object",
+      "properties": {
+        "identity": {
+          "type": "string",
+          "description": "The identity of the worker or client that requested the termination."
+        }
+      }
     },
     "v1TimeSkippingConfig": {
       "type": "object",

openapi/openapiv3.yaml

@@ -9144,6 +9144,9 @@ components:
       properties:
         details:
           $ref: '#/components/schemas/Payloads'
+        identity:
+          type: string
+          description: The identity of the worker or client that requested the cancellation.
     ChildWorkflowExecutionCanceledEventAttributes:
       type: object
       properties:
@@ -14957,7 +14960,10 @@ components:
       properties: {}
     TerminatedFailureInfo:
       type: object
-      properties: {}
+      properties:
+        identity:
+          type: string
+          description: The identity of the worker or client that requested the termination.
     TimeSkippingConfig:
       type: object
       properties:

temporal/api/failure/v1/message.proto

@@ -35,9 +35,13 @@ message TimeoutFailureInfo {
 
 message CanceledFailureInfo {
     temporal.api.common.v1.Payloads details = 1;
+    // The identity of the worker or client that requested the cancellation.
+    string identity = 2;
 }
 
 message TerminatedFailureInfo {
+    // The identity of the worker or client that requested the termination.
+    string identity = 1;
 }
 
 message ServerFailureInfo {