monitoring task per import

[mattiagiupponi]

To avoid zombie execution is essential to set a timeout.
Due to the architecture of the importer, it is not possible to rely on the task timeout because:

• each time a new task is launched
• we need to keep consistency for the whole execution, not for a single task.

The base idea discussed with @giohappy is having a monitoring task.

The monitoring task:

• is going to be launched along with the import, it will control that the last heartbeat of the execution is lower than the timeout set (example 10 min)
• will set the execution as failed if needed
• will die as soon as the execution is successful / invalid or finished

This is just a base idea, the details need a deeper discussion also with @etj