Let a module declare a log the controller creates and never removes (ADR 0297)

The issue tracker's history lasts seven days on the events stream and its
bucket fills toward a cap with no warning (issues 501, 502). A module may
now declare `logs`; the controller creates each as a stream on the bus
(create-or-update, never deleted or recreated, reported when undeclared),
issues it to the owner's assignments in their membership, grants the
runtime exactly the append and direct-read subjects, and raises a
condition when any module's bucket or log reaches 75% of its cap, cleared
below 70%.

cmd/mesh-controller/plain_words.go

@@ -606,6 +606,13 @@ var plainWordings = map[string]func(conditions.Observation) words{
 			Explanation: "The bus refused messages from a part of the mesh, so what they carried did not happen.",
 			Resolved:    "Resolved: the bus takes the messages again"}
 	}),
+	kindStoreFilling: worded(func(o conditions.Observation) words {
+		return words{Headline: "A module's store on the bus is filling up",
+			Needs: "decide whether to raise its cap or have the module keep less.",
+			Explanation: "A bucket or log a module keeps on the bus holds three quarters of its cap or more. When it " +
+				"is full, the bus refuses what the module writes there.",
+			Resolved: "The store has room again"}
+	}),
 	"stream-wrong": worded(func(o conditions.Observation) words {
 		return words{Headline: "Part of the bus's storage is wrong",
 			Needs:       "check the machine the bus runs on; the details say what is missing.",