docs: release notes for the v18.2.21 release #1850

Job	Run time
list	25s
workflow (devkit-core-tests-rerun)	1m 16s
workflow (build-cli)	1m 37s
workflow (modules-builder-tests)	1m 44s
workflow (devkit-core-tests)	1m 26s
workflow (build-unit-tests)	2m 36s
	9m 4s

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