Add parameters to BUFR plugin output section

It would be nice to be able to set the parameters below via the configuration file: WMO_BUFR_HEADER_CENTRE, WMO_DATA_CATEGORY, and WMO_INTERNATIONAL_DATA_SUBCATEGORY
The parameters are used in libcodes.cc and a documentation can be found in the Common Code Table C of the Manual on Codes or at https://github.com/wmo-im/CCT/tree/master.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information