Improve Dynamic attributes section

[ilushaaa]

https://docs.jmix.io/jmix/dyn-attr/dynattr-managing.html

The Is default checkbox signifies that this category will be automatically chosen for a new instance if the entity implements the Categorized interface. If the entity does not implement Categorized, the checkbox value is irrelevant, and you have the flexibility to create either a single category for the entity or multiple categories. In both cases, the attributes will be showcased based on the visibility settings.

It is not entirely clear from the above text in which scenarios an entity should implement the Categorized interface and in which scenarios it should not.

It is quite possible that we need an example of an entity with an implemented interface.