refactor(layers/prometheus-client): provide builder APIs #1650

Job	Run time
check_clippy	3m 34s
check_docs	3m 8s
build_all_features	4m 41s
build_all_platforms (ubuntu-latest)	2m 35s
build_default_features (ubuntu-latest)	48s
build_all_platforms (macos-latest)	2m 27s
build_under_wasm	46s
build_default_features (macos-latest)	38s
build_all_platforms (windows-latest)	4m 35s
build_default_features (windows-latest)	1m 37s
check_msrv	31s
unit	6m 20s
	31m 40s

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