Use keyset pagination in Gitlab lister

Gitlab lister currently lists projects hosted on an instance using offset pagination when querying Gitlab REST API.

However, due to performance issues, a maximum allowed offset has been set (50000 for gitlab.com for instance), resulting to a partial projects listing when reaching it.

Fortunately, a more efficient pagination technique has recently been implemented in Gitlab: keyset pagination.

We should modify the lister implementation to use it in order to be able to list all projects hosted on a gitlab instance again.

For the record, I have tested on the instances we are currently listing in production (T1139) and keyset pagination is supported for all of them.

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Migrated from T2994 (view on Phabricator)