neutron 21.0.0 release

meta:version: 21.0.0
meta:diff-start: 20.0.0.0rc1
meta:series: zed
meta:release-type: release
meta:pypi: no
meta:first: yes
meta:release:Author: Előd Illés <elod.illes@est.tech>
meta:release:Commit: Előd Illés <elod.illes@est.tech>
meta:release:Change-Id: I89c7eb88c86f012536713e1ad7aa5b243aaf7f83
meta:release:Code-Review+1: Lajos Katona <katonalala@gmail.com>
meta:release:Code-Review+1: Boxiang Zhu <zhu.boxiang@99cloud.net>
meta:release:Code-Review+1: Roman Dobosz <gryf73@gmail.com>
meta:release:Code-Review+1: Michael Johnson <johnsomor@gmail.com>
meta:release:Code-Review+1: Brin Zhang <zhangbailin@inspur.com>
meta:release:Code-Review+1: chenker <chen.ke14@zte.com.cn>
meta:release:Code-Review+1: Yasufumi Ogawa <yasufum.o@gmail.com>
meta:release:Code-Review+1: Rajat Dhasmana <rajatdhasmana@gmail.com>
meta:release:Code-Review+1: Pranali Deore <pdeore@redhat.com>
meta:release:Code-Review+1: Sylvain Bauza <sbauza@redhat.com>
meta:release:Code-Review+1: sean mooney <smooney@redhat.com>
meta:release:Code-Review+1: Martin Chacon Piza <martin@chaconpiza.com>
meta:release:Code-Review+1: Takashi Natsume <takanattie@gmail.com>
meta:release:Code-Review+1: Takashi Kajinami <tkajinam@redhat.com>
meta:release:Code-Review+2: Elod Illes <elod.illes@est.tech>
meta:release:Code-Review+2: Hervé Beraud <herveberaud.pro@gmail.com>
meta:release:Workflow+1: Elod Illes <elod.illes@est.tech>
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