feat(@schematics/angular): set `packageManager` in `package.json` on … #1951

Job	Run time
list	26s
workflow (devkit-core-tests)	1m 13s
workflow (modules-builder-tests)	1m 51s
workflow (build-cli)	1m 47s
workflow (devkit-core-tests-rerun)	1m 18s
workflow (build-unit-tests)	2m 14s
	8m 49s

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