Allow columns to be defined as simple symbols

When both the header and the data are defaulting to an AR attribute
passing just the symbol should suffice.

admin/app/components/solidus_admin/ui/table/component.rb

@@ -11,7 +11,9 @@ class Data < Struct.new(:rows, :class, :url, :prev, :next, :columns, :fade, :bat
     def initialize(**args)
       super
 
-      self.columns = columns.map { |column| Column.new(wrap: false, **column) }
+      self.columns = columns.map do |column|
+        column.is_a?(Symbol) ? Column.new(wrap: false, header: column, data: column) : Column.new(wrap: false, **column)
+      end
       self.batch_actions = batch_actions.to_a.map { |action| BatchAction.new(**action) }
     end