Blog: v21.3.0 release post (#6152)

* Blog: v21.3.0 release post

Refs: nodejs/node#50954

* Apply suggestions from code review

Co-authored-by: Richard Lau <rlau@redhat.com>
Signed-off-by: Rafael Gonzaga <rafael.nunu@hotmail.com>

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Signed-off-by: Rafael Gonzaga <rafael.nunu@hotmail.com>
Co-authored-by: Richard Lau <rlau@redhat.com>

Author: RafaelGSS