feat(core/services-gcs): support user defined metadata #1952

Job	Run time
build_all_features	5m 3s
build_all_platforms (ubuntu-latest)	2m 35s
build_all_platforms (macos-latest)	2m 23s
build_default_features (ubuntu-latest)	41s
build_all_platforms (windows-latest)	6m 13s
build_default_features (macos-latest)	39s
build_under_wasm	1m 4s
check_clippy	3m 47s
build_default_features (windows-latest)	2m 42s
check_docs	3m 23s
check_msrv	33s
unit	6m 55s
	35m 58s

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