files: ability to upload and manage files

config/packages/vich_uploader.yaml

config/services.yaml

src/Admin/FileAdmin.php

src/Document/AbstractFile.php

src/Document/EmbeddedImage.php

src/Document/File.php

src/Services/UploadDirectoryNamer.php

src/Services/UploadFileNamer.php

translations/admin+intl-icu.fr.yaml