topology: wake the vacuum dispatcher when a worker frees quota (#11436)

* topology: wake the vacuum dispatcher when a worker frees quota

The dispatch loop slept a fixed 10s whenever every pending volume was
waiting for a per-server quota slot, so a sweep took volumes x 10s
regardless of how fast the compactions were. Workers now signal on a
buffered channel after crediting quota; the dispatcher waits on it with
the 10s sleep kept only as a timeout.

* master: add -vacuumIntervalSeconds to tune the automatic sweep interval

The 14-minute base interval was a literal inside the refresh loop while
every neighbouring vacuum knob was already a flag. Defaults to 840s,
unchanged.

* topology: keep the 14 minute floor on the vacuum interval

A zero-valued MasterOption or a negative -vacuumIntervalSeconds left the
sweep sleeping only its jitter, so treat non-positive intervals as the
previous default.

weed/command/master_follower.go

@@ -47,6 +47,7 @@ func init() {
 	mf.metricsIntervalSec = aws.Int(0)
 	mf.raftResumeState = aws.Bool(false)
 	mf.maxParallelVacuumPerServer = aws.Int(1)
+	mf.vacuumIntervalSeconds = aws.Int(840)
 	mf.telemetryUrl = aws.String("https://telemetry.seaweedfs.com/api/collect")
 	mf.telemetryEnabled = aws.Bool(false)
 }