Ported cpu_monitor to ROS2 #11

Job	Run time
diagnostic_aggregator on humble	3m 59s
diagnostic_aggregator on iron	4m 6s
diagnostic_aggregator on rolling	4m 10s
diagnostic_common_diagnostics on humble	4m 18s
diagnostic_common_diagnostics on iron	4m 8s
diagnostic_common_diagnostics on rolling	4m 10s
diagnostic_updater on humble	3m 51s
diagnostic_updater on iron	4m 7s
diagnostic_updater on rolling	3m 34s
self_test on humble	3m 8s
self_test on iron	4m 15s
self_test on rolling	3m 40s
	47m 26s

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