Add actions to stop & restart a ponos task

Depends on https://gitlab.com/arkindex/ponos/-/issues/94

We need a single new action button on the task header, just before "Raw logs":

• "Stop task" when the task is running
• "Restart task" when the task is in a final state

Clicking on the button would trigger a call to PartialUpdateTask, to update the state task accordingly.