Docs for re-usable filters

[tabacitu]

In Laravel-Backpack/CRUD#5714 and https://github.com/Laravel-Backpack/PRO/pull/296 we added the ability to re-use filters in non-CRUD pages. But we don't have that documented anywhere. We need CLEAR instructions on how someone can do that. NOW, before we forget.

Todo:

• add a section called "How to use Filters on any admin panel page" to the Filters docs page; i would mention you can create a custom page (and link to that section), then how to add filters to that section, to filter some custom things they have there; a dashboard could be a good example; or perhaps a page that has a simple table (aka static table report);
• fill in the section in the Release Notes with a quick mention and maybe some code on how to easily do that;