docs: release notes for the v21.1.5 release #3052

Job	Run time
list	20s
workflow (modules-builder-tests)	2m 4s
workflow (build-unit-tests)	2m 30s
workflow (devkit-core-tests-rerun)	1m 20s
workflow (devkit-core-tests)	1m 36s
workflow (build-cli)	1m 38s
	9m 28s

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