Miscellaneous corrections and improvements

Correction to spawn correctly the R forecasting subprocess from Python in Linux (and not only in Windows) Improvement of the command used to start the forecasting process, in order to flush python output and obtain logs immediately when published Logging and business logic improvement in forecasts to warn about the availability of data with a timestamp equal to or newer compared to the timestamp of the requested prediction time, and nevertheless return the last available timestamp in the dataset

Merge request reports