Add config to be able to ignore entity types

If you have an site which already has a lot of content, the install hook can take a while (~3h in our case)

A lot of entity types there we will never import or export to any other site, while others we want to export and import.

Idea here would be to add a hook so a developer can adjust the allowed entity types. Then on all places this is checked.

With this it would be easy to add later a config for this too, but for hook_install a config is too late...