Using gitlab-ci to cache maven repository
To me the easiest route to this would be to have an instance of an artifactory running. There are several choices out there many of which have an open-source, community or free version that would support maven repositories.  Most options will support caching remote repositories (maven central for example) which can then be curated to enforce specific versions of the dependencies through your projects. It will also accept your own dependencies this way you can have a central unique access point for all maven dependencies in your team.

I've personally had success with Sonatype's Nexus (OSS version, or Pro version). There are other choices out there though check them out.

That said, if what you want is to prime the local repository for a new agent you want to provision, you could do so. But frankly, unless you have some real hefty dependencies (say in the GB size range), I would not bother doing so really and just let Maven naturally pull from the local binary repository instead. It makes for a simpler solution that will be more robust in the long run.