docs: release notes for the v21.2.0 release #3087

Job	Run time
list	20s
workflow (modules-builder-tests)	1m 54s
workflow (devkit-core-tests)	1m 24s
workflow (build-cli)	1m 46s
workflow (build-unit-tests)	2m 51s
workflow (devkit-core-tests-rerun)	1m 30s
	9m 45s

Provide feedback