Keep a condition's looks in the store, so a look that changes nothing writes no bucket (issue 420)

Every look rewrote the condition's value in the conditions bucket, because the
value carried the count of looks, the last look and the newest evidence: 131 647
writes in four days for twelve open conditions, against ADR 0289's rule that a
bucket is written only when what it describes changed. The looks now live in the
controller's store (migration 0095, condition_looks), the bucket holds what a
condition says and is written only when that changes, and the conditions verb and
the condition events put the looks back.

cmd/mesh-controller/watchdogs.go

@@ -704,7 +704,7 @@ func later(a, b time.Time) time.Time {
 // self-check, for the serving controller; the returned function stops them. Nil when the store could
 // not be opened, which is said.
 func watchTheMesh(ctx context.Context, open *stores, server *link.Server, bus link.OverNATS) func() {
-	keeper, err := keeperOn(ctx, bus.Conn)
+	keeper, err := keeperOn(ctx, bus.Conn, storeLooks{open.inventory})
 	if err != nil {
 		fmt.Printf("the condition store could NOT be opened, so nothing that goes wrong is kept or said, and "+
 			"status says the conditions cannot be read: %v\n", err)