addurl --json: Include field for added key

(unless the file was added directly to git due to annex.largefiles configuration.)

(Also done by add --json and import --json)

Command/AddUrl.hs

@@ -379,6 +379,7 @@ cleanup u url file key mtmp = case mtmp of
 			)
   where
 	go = do
+		maybeShowJSON [("key", key2file key)]
 		when (isJust mtmp) $
 			logStatus key InfoPresent
 		setUrlPresent u key url