[19.0] fs_attachment: missing size parameter in `_file_read`

[ivantodorovich]

.../enterprise/documents/controllers/documents.py", line 527, in documents_thumbnail_textual
    head = attachment_read(attachment_sudo, size=self.TEXTUAL_THUMBNAIL_SIZE)
File \"/odoo/external-src/enterprise/documents/tools.py\", line 24, in attachment_read
    return attachment._file_read(attachment.store_fname, size=size)
TypeError: IrAttachment._file_read() got an unexpected keyword argument 'size'

Something missed during the 19.0 migration.
We need to align with :

• [IMP] web: add preview for text, xml, json odoo/odoo#206200

[ivantodorovich]

@lmignon