[Example] Add trash functionality to custom entity

[niklasnatter]

What's in this PR?

This PR demonstrates how to integrate a custom entity with the SuluTrashBundle.

[TheCadien]

Did I do something wrong with my plementation or is something missing in the example.

I had to add the following tags to my TrashItemHandler.
sulu_trash.store_trash_item_handler , sulu_trash.restore_trash_item_handler, sulu_trash.restore_configuration_provider

[alexander-schranz]

@TheCadien If you are in a bundle and not in a project you need to add the tags. In a project like here in the sulu demo the tags are automatically added because symfony uses autoconfigure for this in projects.

Which we did define here: https://github.com/sulu/sulu/blob/822b843b51ed99e0d8f90702c3da7f25fc4490c0/src/Sulu/Bundle/TrashBundle/Infrastructure/Symfony/DependencyInjection/SuluTrashExtension.php#L112
And is enabled here in symfony and sulu skeletons: https://github.com/sulu/skeleton/blob/2cb154888d20fd71022b8636a46015649cf05166/config/services.yaml#L10

For bundles it is normal that you don't use autowire or autoconfigure and need to define them manually (see also bundle best practices).

Why the tags are not required we still should add info box about them to the trash bundle documentation: https://docs.sulu.io/en/2.4/bundles/trash.html. Symfony it self is doing that a lot also in there cases. Like

When no autoconfigure is used the following ... tag need to be added to the service definition.

@TheCadien do you want to create a PR for the trash docs?

[TheCadien]

Ahhhh I see.
Yes its for a Bundle :D !

Sure, I'll add an info box to the docs.
Thanks for the explanation @alexander-schranz