kvserverbase: add DisableCountBasedRebalancingIfMMAEnabled

This commit introduces a new cluster setting,
`DisableCountBasedRebalancingIfMMAEnabled`, which allows us to disable range-count
and lease-count based convergence rebalancing when mma is enabled. These forms
of rebalancing can conflict with mma goals and cause thrashing.

Author: wenyihu6

pkg/kv/kvserver/kvserverbase/base.go

@@ -161,6 +161,16 @@ const (
 	LBRebalancingMultiMetric
 )
 
+// DisableCountBasedRebalancingIfMMAEnabled is a setting that controls whether
+// to disable replica and lease count based rebalancing if multi-metric
+// allocator is enabled.
+var DisableCountBasedRebalancingIfMMAEnabled = settings.RegisterBoolSetting(
+	settings.SystemOnly,
+	"kv.allocator.disable_count_based_rebalancing_with_mma.enabled",
+	"whether to disable replica and lease count based rebalancing if multi-metric allocator is enabled",
+	false,
+)
+
 // RangeFeedRefreshInterval is injected from kvserver to avoid import cycles
 // when accessed from kvcoord.
 var RangeFeedRefreshInterval *settings.DurationSetting