lalinference_pipe_utils.py: enable using psd.xml.gz only for distance max calculation
Previously, if we set distance max with psd.xml.gz, we necessarily have to use that for PSD. This patch enables using psd.xml.gz only for distance max calculation. Whether psd.xml.gz is used for PSD is controlled by ignore-gracedb-psd option.
cc: @vivien @john-veitch