mesh-issues and mesh-knowledge: milestones are records of the issue tracker, and progress reads them (ADR 0493 §1 to §4, issue 1781)

mesh-issues keeps each design's milestone in the state milestones (history 5), says milestone-set and
milestone-moved, and serves milestones, milestone-set and milestone-move. An issue's milestone is its own link
of kind milestone, so at most one milestone per issue is checked inside the issue's own write; kind commit
links a fixing commit. The triage links no milestone, pull request or commit. import with milestones=N seeds
a design's table once. mesh-knowledge's progress reads issue-tracker.milestones and its table parse is gone.

Squashed from four commits so the branch history does not carry a compiled bundle that was committed by
mistake (6 MB); the path is now in .gitignore.

modules/mesh-issues/module.json

@@ -13,6 +13,9 @@
         "move",
         "note",
         "link",
+        "milestones",
+        "milestone-set",
+        "milestone-move",
         "import",
         "groom",
         "set",
@@ -33,6 +36,9 @@
         "move",
         "note",
         "link",
+        "milestones",
+        "milestone-set",
+        "milestone-move",
         "import",
         "groom",
         "set",
@@ -52,7 +58,9 @@
     "triaged",
     "ready",
     "ready-to-verify",
-    "reserved"
+    "reserved",
+    "milestone-set",
+    "milestone-moved"
   ],
   "consumes": [
     "mesh-issues.opened",
@@ -81,7 +89,11 @@
     },
     "counters",
     "grooming",
-    "reservations"
+    "reservations",
+    {
+      "name": "milestones",
+      "history": 5
+    }
   ],
   "config": {
     "first-number": {