Improve gitlab crawling methods

[andrew]

Reported by @simkim in email:

The code crawl_respositories goes backward in time with the param id_before.

As I understand it, it allows to sync most recent repos then next batch.

But when you have crawl all repositories of a forge how do you currently get new repositories with higher ids. I don't see any instance of id_after in the code.

[bzg]

Cc @simkim I believe we can close this issue. Do you confirm? Or are there other improvements we can expect?