Openfoam connector assumes Allrun is in case directory

[wk9874]

The way the connector is currently written, it assumes that the Allrun file is inside the case directory. This is not necessarily the case. Indeed in some examples where multiple cases are run as part of the same Allrun file, it is not the case. Although would we want to allow that? Because then multiple different cases would be mixed up into the same run. Maybe we should just enforce that people using the openfoam connector must have an Allrun file inside a specific case.

[wk9874]

Should document that we expect an Allrun to be inside the case directory which you are planning to run. Having one allrun with multiple cases would mean adding results from all cases to the same run which would be confusing. Should document this behaviour.