Merge branch 'ubuntu-20-04-requirements' into 'master'

Add Ubuntu 20.04 to the supported versions

Closes #238541

See merge request gitlab-org/gitlab!40092

doc/install/requirements.md

@@ -11,7 +11,7 @@ as the hardware requirements that are needed to install and use GitLab.
 
 ### Supported Linux distributions
 
-- Ubuntu (16.04/18.04)
+- Ubuntu (16.04/18.04/20.04)
 - Debian (8/9/10)
 - CentOS (6/7/8)
 - openSUSE (Leap 15.1/Enterprise Server 12.2)