[hostmetricsreceiver] add system uptime metric (#35954) #14618

Job	Run time
arm-unittest-matrix (receiver-0)	5m 15s
arm-unittest-matrix (receiver-1)	7m 23s
arm-unittest-matrix (receiver-2)	8m 29s
arm-unittest-matrix (receiver-3)	6m 22s
arm-unittest-matrix (processor-0)	3m 34s
arm-unittest-matrix (processor-1)	4m 40s
arm-unittest-matrix (exporter-0)	3m 4s
arm-unittest-matrix (exporter-1)	8m 53s
arm-unittest-matrix (exporter-2)	3m 58s
arm-unittest-matrix (exporter-3)	4m 59s
arm-unittest-matrix (extension)	5m 3s
arm-unittest-matrix (connector)	3m 52s
arm-unittest-matrix (internal)	5m 27s
arm-unittest-matrix (pkg)	3m 19s
arm-unittest-matrix (cmd-0)	1m 28s
arm-unittest-matrix (cmd-1)	1m 46s
arm-unittest-matrix (other)	4m 26s
arm-unittest	1s
	1h 21m 59s

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