[BSP][RETRIGGER] Retrigger pipelines for BSP MRs

Every time a BSP related MR is merged, the SRCREV.conf file in the
corresponding meta-layer is updated and all other integration MRs in
that meta-layer can no longer be merged due to conflicts. For this
reason we add this steps every time a BSP related MR is merged:
* Search for all open MRs in the same BSP group of the project on which
the MR occurred.
* Retrigger the pipelines for all these MRs, that in turn updates the
integration branches in the meta-layer.
* All the integration MRs in the meta-layer are now mergeable so that if
two or more MRs are merged (tipically U-Boot and Kernel MRs are merged
almost at the same time) no conflict are expected to occur.
* Moreover, this procedure allows to have an integration MR in the
meta-layer always updated with the latest BSP version in the main
branch.

To make this work we also need to change the retrigger job, avoiding the
possibility to run 'check' jobs that are already running and that would
throw an error.