Demonstrate how to add CN extensions

This is a demonstration of merge request and pipeline.

• CN test: rspec-cn unit pg11
• EE test in CN mode: rspec-ee unit pg11-as-if-cn 1/10

See: https://gitlab.com/gitlab-cn/gitlab-cn-enablement/-/issues/18#note_502589941

Closes https://gitlab.com/gitlab-cn/gitlab-cn-enablement/-/issues/41