Add/review crs for BCCA data

Add (or review for accuracy if it already exists) crs information to BCCA datasets, which likely have the same crs (but please check this):

• s3://mdmf/gdp/bcca_cmip3_future.zarr
• s3://mdmf/gdp/bcca_cmip3_historic.zarr
• s3://mdmf/gdp/bcca_cmip5_future.zarr
• s3://mdmf/gdp/bcca_cmip5_historical.zarr

They have the following THREDDS catalog entries, if that is helpful to have:

• https://cida.usgs.gov/thredds/catalog.html?dataset=cida.usgs.gov/cmip3_bcca/future
• https://cida.usgs.gov/thredds/catalog.html?dataset=cida.usgs.gov/cmip3_bcca/historical
• https://cida.usgs.gov/thredds/catalog.html?dataset=cida.usgs.gov/cmip5_bcca/future
• https://cida.usgs.gov/thredds/catalog.html?dataset=cida.usgs.gov/cmip5_bcca/historical