Flow image export: add additional details

[davidwatkins73]

Description

User request

It takes a lot of work to find out for which system a data flow image has been exported. Please add the name and external-id on top of the image and also use it as the filename of the image instead of "undefined". And add the filetype, if possible.

Resourcing

We would like to add this request to the Waltz team's feature backlog