feat: Allow Adding Client Level Attributes to MetricsTracerFactory #6861

Job	Run time
build(8) except for gapic-generator-java	1m 19s
build(21) except self-service clients	1m 29s
build(8) for gapic-generator-java	9m 30s
build (11)	1m 17s
build (17)	1m 7s
compatibility	1m 34s
dependency_analyzer_unit_test	20s
gapic-generator-java-bom	1m 58s
lint	27s
showcase (11)	4m 1s
showcase-clirr	2m 57s
showcase (17)	4m 4s
showcase-native	8m 30s
unmanaged_dependency_check	5m 39s
	44m 12s

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