Add `datadog.cluster_agent.leader_election.is_leader` #20758

Job	Run time
test / compute-matrix / Compute matrix	9s
test / test (linux, ubuntu-22.04, datadog_cluster_agent, Datadog Cluster Agent) / Datadog Cluster Agent	1m 33s
test / check	2s
test / save-event / Save event	5s
test / submit-traces / Submit traces	1m 25s
	3m 14s

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