refactor(ram_monitor): ros2 port #50

Job	Run time
diagnostic_aggregator on humble	3m 50s
diagnostic_aggregator on iron	3m 39s
diagnostic_aggregator on rolling	2m 11s
diagnostic_common_diagnostics on humble	3m 33s
diagnostic_common_diagnostics on iron	3m 45s
diagnostic_common_diagnostics on rolling	2m 15s
diagnostic_updater on humble	3m 24s
diagnostic_updater on iron	3m 17s
diagnostic_updater on rolling	2m 34s
self_test on humble	3m 49s
self_test on iron	3m 34s
self_test on rolling	2m 4s
	37m 55s

Provide feedback