feat: image url migration

registrations can now store image urls, which will be shown at view.html

WebApp/Migrations/ApplicationDbContextModelSnapshot.cs

@@ -232,6 +232,9 @@ namespace WebApp.Migrations
                     b.Property<DateTime>("EventDate")
                         .HasColumnType("timestamp with time zone");
 
+                    b.Property<string>("ImageURL")
+                        .HasColumnType("text");
+
                     b.Property<string>("Location")
                         .IsRequired()
                         .HasColumnType("text");