[FEATURE-REQUEST] Customize the index action and more filters

Hello, I've just discovered the project and I think it is very useful. Thank you for your work.

I'd like to use it in our project but it currently has some limitations, or at least, I didn't understand how to do it after reading the docs. The two most important issues I see are the following:

1. As far as I understand, we can modify the query to show the records in the index view. However, I'd like to customize completely the way the records are fetched. I have functions in our context to get the list of the records that already include authorization, filters, pagination, and other custom functionalities. Furthermore, sometimes our records are not in an Ecto Repository or the schema is not a Queryable table.
A good solution could be to overwrite the whole index action, in a similar way to the insert, update and delete can be overwritten.

2. I also have some filters that I don't want to be columns in the index page, or they are filtered using columns in associated schemas. It seems like the filters are only available for the index columns.
In this case, maybe I need an optional form on the index page to perform custom these custom filters.

Do you think those are features are compatible with your future vision of the proyect? Or maybe do you have good alternatives for them? If so, maybe I can collaborate with the project to integrate them.

Thank you for your time.