CO-1727 Add migration method for letter attachments
CO-1727 Add migration method for letter attachments

eicher31/compassion-modules,ecino/compassion-modules,CompassionCH/compassion-modules,ecino/compassion-modules,CompassionCH/compassion-modules,maxime-beck/compassion-modules,eicher31/compassion-modules,maxime-beck/compassion-modules,eicher31/compassion-modules,ecino/compassion-modules,maxime-beck/compassion-modules,CompassionCH/compassion-modules,ecino/compassion-modules,ecino/compassion-modules,CompassionCH/compassion-modules,maxime-beck/compassion-modules,eicher31/compassion-modules,eicher31/compassion-modules