docs: release notes for the v21.2.7 release #2946

Job	Run time
build	19s
build-e2e-windows	18s
lint	2m 11s
e2e-windows	0s
Browser Compatibility Tests	0s
test	0s
e2e	0s
publish-snapshots	0s
e2e-package-managers	0s
e2e-snapshots	0s
	2m 48s

Provide feedback