docs: release notes for the v21.0.0-next.9 release #2190

Job	Run time
list	28s
workflow (build-unit-tests)	2m 28s
workflow (modules-builder-tests)	1m 47s
workflow (devkit-core-tests)	1m 24s
workflow (devkit-core-tests-rerun)	1m 22s
workflow (build-cli)	2m 17s
	9m 46s

Provide feedback