Resolve api-platform Bolt\Entity\TranslationInterface issue

[I-Valchev]

See #874

[I-Valchev]

To follow up on what I said in #874
It looks like internally api-platform reads through all properties of a API resource class (in this case, Content, Field and Relation) and, for each field type that is an object, tries to import the corresponding class from the same directory.
For example, in Content.php the reference to the fields:

/**
     * @var Collection|Field[]
     *
     * @ApiSubresource(maxDepth=1)
     * @MaxDepth(1)
     *
     * @ORM\OneToMany(
     *     targetEntity="Bolt\Entity\Field",
     *     mappedBy="content",
     *     indexBy="id",
     *     fetch="EAGER",
     *     orphanRemoval=true,
     *     cascade={"persist"}
     * )
     * @ORM\OrderBy({"sortorder": "ASC"})
     */
    private $fields;

is defined as a collection of type Field, so it is looking for that Field type in the same directory, which is /src/Entity

So, for KNP's internal $translations and $newTranslations, etc, it tries to get the classes from /src/Entity, which are not located there.