Ported cpu_monitor to ROS2 #14

Job	Run time
diagnostic_aggregator on humble	3m 52s
diagnostic_aggregator on iron	3m 54s
diagnostic_aggregator on rolling	3m 44s
diagnostic_common_diagnostics on humble	3m 41s
diagnostic_common_diagnostics on iron	3m 46s
diagnostic_common_diagnostics on rolling	3m 56s
diagnostic_updater on humble	3m 14s
diagnostic_updater on iron	3m 33s
diagnostic_updater on rolling	3m 36s
self_test on humble	4m 1s
self_test on iron	4m 26s
self_test on rolling	4m 4s
	45m 47s

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