Block Tabs entities are unavailable as Content reference type

Problem/Motivation

I can create Block Tabs entities normally, but they becomes unavailable as content entities, like "Custom Block", for example.

Steps to reproduce

1. Create Block Tabs entity.
2. In a node type fields try to create an Entity Reference field, and see that there is no "Block Tabs" item in "Content" section, like "Content block"

Proposed resolution

Seems Block Tabs entities are stored as configuration, that limits their use cases. Will be good to provide an option to create Block Tabs as Content entities, instead of configuration entities, like "Custom Block.