Support keyset pagination for API calls

Extracted from https://gitlab.com/gitlab-org/gitlab-ce/issues/42194:

Due to performance reasons, we want to remove support for 'traditional' pagination and encourage the use of keyset pagination. A great blog post and presentation about this can be found here: https://use-the-index-luke.com/no-offset

The proposed change in this issue is:

1. Support keyset pagination in addition to normal pagination
2. When called without pagination parameters, default to normal pagination
3. Keyset pagination support must be requested explicitly (e.g. by including a parameter or header)

For details see MR description in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/18584