fix(@schematics/angular): warn when production configuration is missi… #2951

Job	Run time
list	19s
workflow (modules-builder-tests)	1m 55s
workflow (devkit-core-tests)	1m 12s
workflow (build-unit-tests)	2m 25s
workflow (devkit-core-tests-rerun)	1m 25s
workflow (build-cli)	1m 47s
	9m 3s

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