Ported cpu_monitor to ROS2 #13

Job	Run time
diagnostic_aggregator on humble	3m 28s
diagnostic_aggregator on iron	5m 32s
diagnostic_aggregator on rolling	3m 44s
diagnostic_common_diagnostics on humble	2m 55s
diagnostic_common_diagnostics on iron	3m 34s
diagnostic_common_diagnostics on rolling	3m 22s
diagnostic_updater on humble	3m 9s
diagnostic_updater on iron	3m 5s
diagnostic_updater on rolling	3m 29s
self_test on humble	3m 27s
self_test on iron	3m 45s
self_test on rolling	3m 43s
	43m 13s

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