c2c: reduce TestStreamingAutoReplan runtime

In a suprising twist, cockroachdb#106853 deflaked this test, but also increased the
runtime to 10 minutes. To understand why, consider that the default value of
the stream_replication.replan_flow_frequency setting is 10 minutes, and if the
user changes the cluster setting, the frequency will only take effect on the
next replanning check. So, if a stream begins at t0, and the user changes the
setting at t1, the replanning frequency will actually change 10 minutes after
t0.

In cockroachdb#105853  patch reduced stream_replication.replan_flow_frequency setting to
500 ms _after_ the stream began, which caused the next replanninng check to
occur a full 10 minutes after the stream started! This patch changes this
cluster setting _before_ the stream begins, reducing the runtime of this test
to a speedy 10 seconds.

Epic: none

Release note: none

Author: msbutler

pkg/ccl/streamingccl/streamingest/replication_stream_e2e_test.go

@@ -729,6 +729,7 @@ func TestStreamingAutoReplan(t *testing.T) {
 	defer cleanup()
 	// Don't allow for replanning until the new nodes and scattered table have been created.
 	serverutils.SetClusterSetting(t, c.DestCluster, "stream_replication.replan_flow_threshold", 0)
+	serverutils.SetClusterSetting(t, c.DestCluster, "stream_replication.replan_flow_frequency", time.Millisecond*500)
 
 	// Begin the job on a single source node.
 	producerJobID, ingestionJobID := c.StartStreamReplication(ctx)
@@ -746,7 +747,6 @@ func TestStreamingAutoReplan(t *testing.T) {
 
 	// Configure the ingestion job to replan eagerly.
 	serverutils.SetClusterSetting(t, c.DestCluster, "stream_replication.replan_flow_threshold", 0.1)
-	serverutils.SetClusterSetting(t, c.DestCluster, "stream_replication.replan_flow_frequency", time.Millisecond*500)
 
 	// The ingestion job should eventually retry because it detects new nodes to add to the plan.
 	require.Error(t, <-retryErrorChan, sql.ErrPlanChanged)