feat: Client/StubSettings' getEndpoint() returns the resolved endpoint #5820

Job	Run time
build (11)	12m 49s
build (17)	12m 33s
build(21) except self-service clients	11m 26s
build(8) except for gapic-generator-java	4m 2s
build(8) for gapic-generator-java	9m 32s
compatibility	1m 53s
lint	22s
showcase (11)	3m 58s
showcase (17)	3m 58s
showcase-native	8m 7s
gapic-generator-java-bom	1m 41s
showcase-clirr	3m 5s
unmanaged_dependency_check	3m 17s
	1h 16m 43s

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