feat: Allow Adding Client Level Attributes to MetricsTracerFactory #6914

Job	Run time
build(8) except for gapic-generator-java	44s
build(21) except self-service clients	4m 48s
build (11)	5m 4s
build(8) for gapic-generator-java	1m 53s
build (17)	4m 52s
lint	32s
compatibility	1m 34s
dependency_analyzer_unit_test	18s
gapic-generator-java-bom	1m 48s
showcase (11)	3m 50s
showcase (17)	3m 46s
showcase-clirr	3m 8s
showcase-native	8m 0s
unmanaged_dependency_check	4m 48s
	45m 5s

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