[MR][CLEANUP] Insert script to perform MR cleanup

* This script is necessary for all the open MRs that were created by the
GitBot when performing meta-layers/manifest integration. Indeed, in case the source
MR is closed, the integration one created by the Gitbot remains opened
and shall be closed by hand. The script actually searches for this type
of MRs, close them and delete the source branch.
* This type of job is intended to be executed on a weekly schedule in
order to clean week by week the MR in the Edgehog group.