Out-of-order jobs execution

Thanks to the new needs keyword and the underlying acyclic graph calculation, Gitlab CI is now able to perform jobs in an order different from that specified by the stages: the subsequent stages jobs are triggered as soon as all their dependencies are satisfied, without waiting all the jobs in the current stage to be completed. This way, the pipeline is globally optimized and processed faster.

The purpose of this merge request is to implement in the OTB pipeline this "out-of-order execution" of jobs.