ApiPlatform: change design to expose API through standalone class and use DataProvider and DataPersister

[Rebolon]

Here is the documentation about this:

• https://api-platform.com/docs/core/design/

The problem with current implementation is that ApiPlatform and Doctrine share everything, which could be a problem if we don't want to expose some properties to Api.
In complexe legacy app it cuols be hard to use ApiPlatform with the current implementation. So the separation of concern is, once again, a good thing !

Now the problem is how to implement this ???

[Rebolon]

Should not be closed because !118 is only a POC for DataProvider usage

[Rebolon]

It must also show how to use:

• pagination in this pattern (Provider and object returned by Persister)
• sort
• filter like search
• return only wished params