docs: release notes for the v21.0.1 release #2583

Job	Run time
list	24s
workflow (build-cli)	1m 31s
workflow (modules-builder-tests)	1m 44s
workflow (devkit-core-tests)	1m 32s
workflow (devkit-core-tests-rerun)	1m 30s
workflow (build-unit-tests)	2m 27s
	9m 8s

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