Add timer to kill ERT if no output for 15 minutes

[wouterjdb]

ERT sometimes hangs, see https://github.com/equinor/libres/issues/984.

This PR adds a timer which, after 15 minutes of complete silence from the ERT process, kills it including all child processes.

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• [ ] :tada: This PR closes #ISSUE_NUMBER.
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  • [ ] Task 2
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