Make disk ejection after writing optional

[pb66]

I was sad to see the idea of a option to not eject an sdcard after writing being dismissed so easily in issue #74.

I have been using Balena etcher for some time (with auto ejection turned off) so that I can add ssh and wpa_supplicant files before ejecting and removing the sdcard to put in a Pi. Whilst the option is pretty well hidden on etcher I understand the reasons given in issue #74, however, it could still be done, perhaps by a command line option passed in a desktop shortcut. Users like myself can just modify the shortcut to add the switch which is handled in imager without any confusing options displayed in the GUI.

This one item renders imager unusable to me, I will not keep pulling and pushing an sdcard into the reader slot of my laptop when Balena Etcher does what I need. Please reconsider, as a huge fan of Raspberry Pi I would prefer to use imager.