[DocDB] Remove delay for load balancer after leader failover

[druzac]

Jira Link: DB-14077

Description

The load balancer is not run for the first two minutes after a master leader becomes leader:

yugabyte-db/src/yb/master/catalog_manager_bg_tasks.cc

Lines 261 to 262 in b4b3a40

	if (catalog_manager_->TimeSinceElectedLeader() >
	MonoDelta::FromSeconds(FLAGS_load_balancer_initial_delay_secs)) {

This delay is to wait for the new master leader to receive initial heartbeats from tablet servers. However when the persisted tablet server registry (#22925) is active the full membership of tablet servers in the cluster is available from the sys catalog so new master leaders no longer need to wait for so long. Instead a new master leader could start running the load balancer as soon as it has received a heartbeat from every tablet server considered LIVE in the registry. This should be a few seconds in the common case.

Issue Type

kind/enhancement

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