QGIS is now able to export raster styling to sld, for example to be used in Geoserver. See: https://docs.geoserver.org/latest/en/user/styling/qgis/index.html#exporting-raster-symbology
This feature was funded by OSGeo UK, GeoServer PSC, Brad Hards
This feature was developed by Luigi Pirelli and GeoSolutions