docs: release notes for the v21.2.1 release #2822

Job	Run time
build-e2e-windows	19s
build	18s
lint	1m 57s
Browser Compatibility Tests	0s
test	0s
e2e	0s
e2e-package-managers	0s
publish-snapshots	0s
e2e-snapshots	0s
e2e-windows	0s
	2m 34s

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