Add smooth_radar_mask functionality from steps blending to pca_kalman_filter_blending (#528)

Add smooth_radar_mask functionality from steps blending to pca_ens_kalman_filter blending

Co-authored-by: mats-knmi <145579783+mats-knmi@users.noreply.github.com>
Co-authored-by: m-rempel <martin.rempel@gmx.de>

Author: 3 people