Refactor file store constructor #604

Job	Run time
build	2m 27s
fmt	21s
clippy	2m 11s
tests (coverage-map)	1m 39s
tests (coverage-point-calculator)	1m 55s
tests (ingest)	1m 46s
tests (reward-scheduler)	1m 14s
tests (task-manager)	1m 5s
tests-postgres (boost-manager)	2m 40s
tests-postgres (file-store)	2m 13s
tests-postgres (iot-config)	2m 49s
tests-postgres (iot-packet-verifier)	3m 32s
tests-postgres (iot-verifier)	2m 47s
tests-postgres (mobile-config)	2m 46s
tests-postgres (mobile-packet-verifier)	2m 37s
tests-postgres (mobile-verifier)	3m 11s
build-release	0s
	35m 13s

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