feat(core/services-gcs): support user defined metadata #1988

Job	Run time
build_all_features	5m 7s
build_default_features (ubuntu-latest)	40s
build_default_features (macos-latest)	44s
build_default_features (windows-latest)	1m 19s
check_docs	3m 41s
check_msrv	33s
check_clippy	4m 5s
build_all_platforms (ubuntu-latest)	2m 37s
build_all_platforms (macos-latest)	4m 58s
build_under_wasm	49s
build_all_platforms (windows-latest)	4m 55s
unit	6m 58s
	36m 26s

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