Use Field::RichText type for has_rich_text (#2926)

Detects ActionText rich text associations based on the class name and
attribute when using the generators and set the type to `Field::RichText`.

Fixes #2925

Author: smartygus

lib/generators/administrate/dashboard/dashboard_generator.rb

@@ -128,7 +128,10 @@ def column_types(attr)
 
       def association_type(attribute)
         relationship = klass.reflections[attribute.to_s]
-        if relationship.has_one?
+        if relationship.name.start_with?("rich_text_") &&
+            relationship.options[:class_name]&.start_with?("ActionText::")
+          "Field::RichText"
+        elsif relationship.has_one?
           "Field::HasOne"
         elsif relationship.collection?
           "Field::HasMany"