How to add links to left menu?

Hello. I’ve been running a small self-hosted Gitlab instance (the free one), version 13.2.3.
Today I went to OpenLDAP project: https://git.openldap.org/openldap/openldap and noticed they have an external link to Bugzilla in left menu. I don’t know which version they are running, their “help” page (https://git.openldap.org/help) only says Gitlab Enterprise Edition.

So the question is: are external links a premium feature? If not, then how can I add one myself on my own instance? Thanks in advance!

You can do on the free instance as well! But it’s a project-level property, not an instance once, AFAIK.

You go to your projects -> Settings -> Integrations and enable External Wiki

Thank you!