Add support for atomic add/update of task artifacts

server/schema/services/tasks.conf

@@ -1304,4 +1304,40 @@ ping {
             additionalProperties: false
         }
     }
+}
+
+add_or_update_artifacts {
+    "2.6" {
+        description: """ Update an existing artifact (search by key/mode) or add a new one """
+        request {
+            type: object
+            required: [ task, artifacts ]
+            properties {
+                task {
+                    description: "Task ID"
+                    type: string
+                }
+                artifacts {
+                    description: "Artifacts to add or update"
+                    type: array
+                    items { "$ref": "#/definitions/artifact" }
+                }
+            }
+        }
+        response {
+            type: object
+            properties {
+                added {
+                    description: "Keys of artifacts added"
+                    type: array
+                    items { type: string }
+                }
+                updated {
+                    description: "Keys of artifacts updated"
+                    type: array
+                    items { type: string }
+                }
+            }
+        }
+    }
 }