Envoy 1.21.0 released

[Alyssa (Rzeszutek) Wilk]

Hey folks,

The time has come for the quarterly build, so we have tagged and released Envoy 1.21.0!
Release: https://github.com/envoyproxy/envoy/releases/tag/v1.21.0
Docker images will be pushed within the hour: https://hub.docker.com/u/envoyproxy/
Docs: https://www.envoyproxy.io/docs/envoy/v1.21.0/
Release notes: https://www.envoyproxy.io/docs/envoy/v1.21.0/version_history/current

As a reminder we've shifted our release schedule by 15d, so most releases will be cut 2 weeks into the quarter from here on out.

Some stats since the last release:
envoy: 514 commits from 126 contributors
(If you are into cool contributor stats check out https://envoy.devstats.cncf.io/)

As always a monumental, thank you to all of our wonderful users, contributors, and maintainers help to make Envoy such a tremendous success.

Thanks,
Alyssa, on behalf of the Envoy maintainer team