Offset for observation files

[s7yoewer]

For long simulations, the model often has to be restarted as the wallclock time is not large enough. An idea would be to include an offset in the enkfpf.par file so that one does not have to generate observations files with the right numbering from the restarting point onwards.

E.g. when I assimilate daily, I will have 365 observation files per year. When my model runs for 10 years and then I want to restart it from there, I would need to generate a new folder so that observation 3651 now has the numbering .00001 so that it is assimilated first. An offset flag that I can set to 3650 would make sense as I can use the same observation folder. Maybe it makes sense to include this in the next_observation_pdaf.F90 and the input parameter file.