Enable discovery manager metrics in target allocator #5271

Job	Run time
End-to-end tests (1.23, e2e)	15m 34s
End-to-end tests (1.23, e2e-instrumentation)	14m 29s
End-to-end tests (1.23, e2e-upgrade)	14m 28s
End-to-end tests (1.23, e2e-prometheuscr)	13m 15s
End-to-end tests (1.23, e2e-autoscale)	16m 10s
End-to-end tests (1.28, e2e)	15m 21s
End-to-end tests (1.28, e2e-instrumentation)	17m 35s
End-to-end tests (1.28, e2e-upgrade)	13m 7s
End-to-end tests (1.28, e2e-prometheuscr)	12m 59s
End-to-end tests (1.28, e2e-autoscale)	14m 19s
e2e-tests-check	2s
	2h 27m 19s

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