[Fetch remote repositories repo] is missing when using gitlab

[mritd]

What happened:

When using gitlab, the number of repositories displayed on the UI interface is incorrect after clicking the [Fetch remote repositories repo] button

What you expected to happen:

The UI interface can correctly display the number of warehouses.

How to reproduce it (as minimally and precisely as possible):

Only need to connect to gitlab correctly, and the current user has more than 50 (not completely accurate) repositories on gitlab.

Anything else we need to know?:

After reading the source code, agloa uses github.com/xanzy/go-gitlab as the gitlab connection client; but by default go-gitlab will not handle paging, which results in repo that exceeds one page will not be displayed.

Reference source code: https://github.com/agola-io/agola/blob/master/internal/gitsources/gitlab/gitlab.go#L281

Environment:

• Agola version: master
• Agola running environment (if useful to understand the bug): docker
• Others:

[sgotti]

@mritd Thanks for the report! Since you've already discovered the issues, would you like to open a Pull Request?