[otci] add link metrics commands to otci #572

Job	Run time
backbone-router	13m 53s
BR (mDNSResponder, TREL=0)	30m 32s
BR (mDNSResponder, TREL=1)	31m 1s
BR MATN (mDNSResponder, TREL=0)	19m 40s
BR LowPower (mDNSResponder, TREL=0)	8m 50s
BR nat64 (mDNSResponder, TREL=0)	24m 35s
BR (avahi, TREL=0)	31m 15s
BR (avahi, TREL=1)	30m 30s
BR core-firewall (avahi, TREL=0)	30m 56s
upload-coverage	52s
	3h 42m 4s

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