fix: use dynamic tracer name instead of hardcoded gax-java #255

Job	Run time
filter	54s
build(21) except self-service clients	1m 40s
build(25) except self-service clients	1m 46s
build (11)	1m 56s
build(8) except for gapic-generator-java	1m 58s
dependency_analyzer_unit_test	1m 28s
unmanaged_dependency_check	7m 58s
gapic-generator-java-bom	2m 4s
build(8) for gapic-generator-java	11m 30s
build (17)	1m 50s
build(8) for showcase	9m 5s
showcase (11)	10m 8s
showcase-clirr	5m 58s
showcase (25)	10m 4s
showcase (21)	10m 30s
showcase (17)	9m 57s
	1h 28m 46s

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