Apache Beam 2.22.0 Release

[Gradle Release Plugin] - creating tag: 'v2.22.0-RC1'.

Tag Beam 2.21.0 release.

2.21.0 release candidate apache#1.

Website transitioned from Jekyll to Hugo. See BEAM-9876.

2.20.0

Tag for Green Dataflow Runner V2.

[Gradle Release Plugin] - creating tag: 'v2.20.0-RC2'.

[Gradle Release Plugin] - creating tag: 'v2.20.0-RC1'.

Copy the v2.19.0-RC1 to v2.19.0