One unintended consequence applying a schema to the configuration was
that the var_name field was overlooked and therefore multiple single-band
GeoTIFFs as output was unintentionally ruled out.
Add var_name to the allowed list of fields in file_path_template
Fix band numbering code to allow single-band GeoTIFFs
One unintended consequence applying a schema to the configuration was that the
var_namefield was overlooked and therefore multiple single-band GeoTIFFs as output was unintentionally ruled out.var_nameto the allowed list of fields infile_path_template.yamlfor the single-band case