Display the original task of a restart

https://redmine.teklia.com/issues/6515

Requires backend#1711 (closed)

When a task has an original_task_id set, the frontend should display the slug of the restarted task in the task header.

This could be done by adding (restart of task_slug) in the header, but it's already quite long: we could end up with something like "offline_dan_generic_models_4f2794_2 on iccos + NVIDIA GeForce RTX 2060 with the farm 'Pre-Production' (restart of offline_dan_generic_models_4f2794)".

Since the farm is already shown in the process' header, and can be guessed from the agent's hostname, we can remove with the farm … to shorten this header and make space for this original task slug.