pythonic extended filenames

Proposed changes

Let's consider a classic python clode:

resampled.write(
    'output.tif', 
    pixel_type='uint16', 
    ext_fname='nodata=65535&gdal:co:COMPRESS=DEFLATE&gdal:co:TILED=YES&gdal:co:BIGTIFF=YES'
)

Here ext_fname could be str | dict to enable doing the following:

ext_fname = {
    "nodata": 65535,
    "gdal:co:COMPRESS": "DEFLATE",
    "gdal:co:TILED": "YES",
    "gdal:co:BIGTIFF": "YES"
}
resampled.write(
    'output.tif', 
    pixel_type='uint16', 
    ext_fname=ext_fname
)

This could be nice to enable/disable in a more flexible manner extended filename options.