fix: space/blob/list ok type (#79)

The ok type for `space/blob/list` contains a `cause` field with the CID
of the task that caused the blob to be stored.

Author: alanshaw

capabilities/space/blob/blob.ipldsch

@@ -29,6 +29,7 @@ type ListOk struct {
 
 type ListBlobItem struct {
     blob Blob
+    cause Link
     insertedAt ISO8601Date
 }
 

capabilities/space/blob/list.go

@@ -43,6 +43,7 @@ type ListOk struct {
 
 type ListBlobItem struct {
 	Blob       types.Blob
+	Cause      ipld.Link
 	InsertedAt time.Time
 }
 

capabilities/space/blob/list_test.go

@@ -35,13 +35,15 @@ func TestRoundTripListOk(t *testing.T) {
 				Digest: testutil.RandomMultihash(t),
 				Size:   uint64(1024),
 			},
+			Cause:      testutil.RandomCID(t),
 			InsertedAt: time.Now().UTC().Truncate(time.Second),
 		},
 		{
 			Blob: types.Blob{
 				Digest: testutil.RandomMultihash(t),
 				Size:   uint64(2048),
 			},
+			Cause:      testutil.RandomCID(t),
 			InsertedAt: time.Now().UTC().Truncate(time.Second),
 		},
 	}