tests: Add metrics showcase tests for timeout case #18699

Job	Run time
windows	2m 15s
gapic-libraries-bom	18m 33s
generation-config-check	1m 42s
enforcer	19m 8s
bulk-filter	1m 0s
lint	41m 6s
changes	3s
split-units (sdk-platform-java, 8)	4m 11s
split-units (sdk-platform-java, 11)	4m 31s
split-units (sdk-platform-java, 17)	4m 21s
split-units (sdk-platform-java, 25)	4m 19s
split-units (sdk-platform-java, 21)	4m 17s
units (8)	41m 47s
units (21)	33m 33s
units (17)	33m 3s
units (11)	42m 56s
units (25)	33m 10s
	4h 49m 55s

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