docs: release notes for the v21.1.0 release #2865

Job	Run time
list	30s
workflow (build-cli)	1m 51s
workflow (build-unit-tests)	2m 36s
workflow (devkit-core-tests-rerun)	1m 37s
workflow (devkit-core-tests)	1m 25s
workflow (modules-builder-tests)	1m 54s
	9m 53s

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