docs: release notes for the v21.2.0-rc.2 release #3058

Job	Run time
list	24s
workflow (devkit-core-tests)	1m 20s
workflow (build-cli)	1m 41s
workflow (build-unit-tests)	2m 37s
workflow (modules-builder-tests)	1m 54s
workflow (devkit-core-tests-rerun)	1m 31s
	9m 27s

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