docs: release notes for the v21.0.6 release #2618

Job	Run time
build-e2e-windows	39s
build	33s
lint	2m 13s
test	0s
publish-snapshots	0s
e2e	0s
Browser Compatibility Tests	0s
e2e-package-managers	0s
e2e-snapshots	-1s
e2e-windows	-1s
	3m 23s

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