Keep what a consumer gives up on until a person delivers it again or drops it

Design 25 promised a dead-letter stream that did not exist: a message a
consumer gave up on stayed only in its source, which drops it after a week,
and its condition cleared when the advisories stopped (hq issue 330, ADR 0264).

module.json

@@ -71,6 +71,7 @@
     "bus",
     "retire",
     "cleanup",
+    "dead-letters",
     "data",
     "build",
     "artifacts",