mmaprototype: make numtopkreplicas configurable in test

It was hard-coded to two (in the test), but I want to be able to change it for
an improved lease rebalancing test that I'm adding.

Author: tbg

pkg/kv/kvserver/allocator/mmaprototype/cluster_state_test.go

@@ -444,7 +444,11 @@ func TestClusterState(t *testing.T) {
 
 				case "store-leaseholder-msg":
 					msg := parseStoreLeaseholderMsg(t, d.Input)
-					cs.processStoreLeaseholderMsgInternal(context.Background(), &msg, 2, nil)
+					n := numTopKReplicas
+					if o, ok := dd.ScanArgOpt[int](t, d, "num-top-k-replicas"); ok {
+						n = o
+					}
+					cs.processStoreLeaseholderMsgInternal(context.Background(), &msg, n, nil)
 					return ""
 
 				case "make-pending-changes":

pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/multiple_ranges.txt

@@ -17,7 +17,7 @@ store-load-msg
 ----
 
 # Range 4 has the highest cpu on the leaseholder, and range 3 the highest cpu on a follower.
-store-leaseholder-msg
+store-leaseholder-msg num-top-k-replicas=2
 store-id=1
   range-id=1 load=[10,10,20] raft-cpu=5 config=(num_replicas=3 constraints={'+region=us-west-1:1'} voter_constraints={'+region=us-west-1:1'})
     store-id=1 replica-id=1 type=VOTER_FULL leaseholder=true