refactor(layers/prometheus-client): provide builder APIs similar to `PrometheusLayer` #1540

Job	Run time
check_clippy	3m 24s
check_docs	3m 29s
build_all_features	4m 38s
build_default_features (ubuntu-latest)	40s
check_msrv	36s
build_default_features (macos-latest)	35s
build_all_platforms (ubuntu-latest)	2m 17s
build_under_wasm	45s
build_default_features (windows-latest)	1m 35s
unit	6m 38s
build_all_platforms (macos-latest)	2m 0s
build_all_platforms (windows-latest)	4m 54s
	31m 31s

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