Add FileField for Files.

[bytes-max]

There are constraint issues when attempting to upload a PDF file trough the only "Upload" field there is right now: ImageField. As stated in this task, it might be valuable to have a middle-class (FileField) that is just extended by the ImageField.

[Seb33300]

Even if the ImageField is not really suitable for other type of field, you can override the image constraint on the ImageField like this if you still want to upload something else:

ImageField::new(...)
    ->setFileConstraints(new Assert\File(['extensions' => 'pdf']))

But I agree a new FileField is welcome

[bytes-max]

Overriding alone is not sufficient, as it will cause other issues in the core code as far as I remember, since I've tried that before if I am not mistaken... :(

[bytes-max]

I was in need for this again, so I just created my own plugin that can do it without any further ado.

If people want to have it, they can refer to this repo: https://packagist.org/packages/bytescommerce/easy-admin-file-upload-field