I would like to add a new field type in my content type. The field is of the type List(Text) and the possible values should be the list of user roles in the system. Is there a way to do it without creating a custom field type?
You can try using Role Field module..
Project page says
Role Field provides a field for selecting roles that exist in your site.
Please note that there is no out-of-the-box permissions shenanigans going on. It just lets you pick from a list of roles. Although, combined with Rules the possibilities are pretty interesting.