Add `datadog.cluster_agent.leader_election.is_leader` #20759

Job	Run time
test / compute-matrix / Compute matrix	10s
test / test (linux, ubuntu-22.04, datadog_cluster_agent, Datadog Cluster Agent) / Datadog Cluster Agent	1m 32s
test / check	4s
test / save-event / Save event	3s
test / submit-traces / Submit traces	1m 1s
	2m 50s

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