(EE) Create repositories via Gitaly

Merged Jacob Vosmaer (GitLab) requested to merge ee-gitaly-create-repository into master

What does this MR do?

GitLab-EE counterpart to https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/14566

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

What are the relevant issue numbers?