[FSTORE-1489] make prefix in required serving key mandatory #485

Job	Run time
Lint and Stylecheck	12s
Unit Tests (3.8)	2m 2s
Unit Tests (No Optional Dependencies)	1m 40s
Unit Tests (Pandas 1.x)	1m 36s
Unit Tests (3.9)	2m 14s
Unit Tests (Local TZ)	2m 32s
Unit Tests (3.10)	2m 25s
Unit Tests (Typechecked)	2m 20s
Unit Tests (Windows)	8m 45s
Unit Tests (Windows) (Local TZ)	9m 40s
	33m 26s

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