fix(@schematics/angular): warn when production configuration is missi… #1606

Job	Run time
list	23s
workflow (build-cli)	24s
workflow (build-unit-tests)	27s
workflow (devkit-core-tests-rerun)	27s
workflow (modules-builder-tests)	21s
workflow (devkit-core-tests)	27s
	2m 29s

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