allow setting tiff SoftwareTag, DocumentNameTag, ImageDescTag

[jdries]

There's a number of tiff tags that currently can not be written to geotiff in Geotrellis. For instance: SoftwareTag, DocumentNameTag, ImageDescTag These are already defined here: https://github.com/locationtech/geotrellis/blob/fa88aeddab0849cdb8f830d3747554bc7adceb1f/raster/src/main/scala/geotrellis/raster/io/geotiff/tags/codes/TagCodes.scala#L33

The request is to either add explicit support for these tags, or to allow a more generic way to customize the tags that are written so that we can add any tag.