docs: release notes for the v21.2.10 release #3034

Job	Run time
build-e2e-windows	23s
build	29s
lint	1m 57s
test	0s
publish-snapshots	0s
Browser Compatibility Tests	0s
e2e-snapshots	0s
e2e	0s
e2e-package-managers	0s
e2e-windows	-1s
	2m 48s

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