harcoded productDefinitionTemplateNumber when a perturbation Number value is found

[cosunae]

Hi
I stumbled upon this while trying to write some data that contained a "number" coordinate.

cfgrib/cfgrib/xarray_to_grib.py

Line 125 in 2707106

 detected_grib_keys["productDefinitionTemplateNumber"] = 1 

It will set the productDefinitionTemplateNumber to 1.
The issue is that there are many other productDefinitionTemplateNumber's that can contain a perturbation Number,
and this seems to erase the value already set by the user in the dataset.