GitLab wiki is a great tool to maintain documentation. It comes with a convenient web interface as well as wiki repository (Git Access) in order to edit the wiki.
Unfortunately, when adding attachments to an article via the web interface, the attachment will not be saved inside of the wiki repository (Git Access). Is there a way to add attachment to wiki without using the Git Access?
To put it bluntly, no there isn't. (At least not yet, as of version 8.9) Files which are uploaded as Attachment are being put in a uploads/ folder which is global.