[gitlab] Update git_data_dir to latest format

[lambertjosh]

We need to update the git_data_dir setting to use the newer format, as the current one is deprecated and will stop working in 10.0.

We need to switch git_data_dir '/gitlab-data/git-data'; to git_data_dirs({ "default" => { "path" => "/gitlab-data/git-data" } });.

[joerg84]

Can you make a PR @lambertjosh