Delay the initialization of resource columns until needed
Delay the initialization of resource columns until needed

At the point of initialization, when running migrations and the table did not exist for the resource
class at that point, it would fail with the following error:

```
ActiveRecord::StatementInvalid: <database-adapter>::UndefinedTable: ERROR:  relation
"<table-name-for-model>" does not exist
```

ivannovosad/activeadmin-axlsx