Add 'ref' field for gitlab_project_repository table

[dvaneson]

I'd like to be able to specify the branch to use for the gitlab_project_repository table, as right now it can only ever get the file tree from the default branch from a repository.

I see in the Gitlab API Wrapper library that there is a Ref option that can be used with the ListTree API call: https://github.com/xanzy/go-gitlab/blob/main/repositories.go#L54

[graza-io]

Thanks, this will be in v0.7.0 - may take some time as I want to get dependencies updated also and the GitLab SDK has a few changes that require some attention ;)