Add S3 backend to cloudsync #2699

Job	Run time
msys2-build-test (CLANG64, windows-latest)	7m 49s
msys2-build-test (CLANGARM64, windows-11-arm)	11m 47s
msys2-build-test (MINGW64, windows-latest)	9m 26s
msys2-build-test (UCRT64, windows-latest)	8m 28s
	37m 30s

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