[FSSDK-11528] Holdout support in decision service #1290

Job	Run time
lint	1m 23s
unit_tests (18)	1m 47s
lint_markdown_files / lint	53s
unit_tests (24)	1m 31s
integration_tests / test	7s
unit_tests (20)	1m 46s
unit_tests (22)	1m 45s
fullstack_production_suite / test	5s
Coveralls coverage	-1s
	9m 16s

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