feat: Add ChannelPoolSettings Getter for gRPC's ChannelProvider #5889

Job	Run time
build(21) except self-service clients	11m 25s
build (11)	13m 23s
build (17)	12m 31s
build(8) except for gapic-generator-java	4m 1s
build(8) for gapic-generator-java	9m 30s
compatibility	1m 33s
gapic-generator-java-bom	1m 39s
lint	27s
showcase (11)	4m 2s
showcase-clirr	3m 22s
showcase (17)	4m 6s
showcase-native	8m 23s
unmanaged_dependency_check	5m 58s
	1h 20m 20s

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