optionally allow image resolution by name

[oneingan]

this enables a use case where one would continuously update the image and re-create it as a new snapshot, causing the id to constantly change but the name to be persistent. since ordinarily name is a really poor way to resolve images, in particular also because we always need to talk to the api to get the actual image, this entire feature is limited to user images rather than all images. specifically this also lessens the API work we need to do.

the template config has a new checkbox to enable this feature, which then prompts a reload of the image combobox to only include user images (and at the same time the values in the model are changed from slugOrIds to names)

at provisioning time we then need to pass a bit more context along so as to resolve accordingly in newImage()

Testing done

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[halkeye]

oh man, i so rarely use jenkins anymore, but i had so much trouble testing the other PR because I have way too many images.

[oneingan]

Oh! thanks for your reply. If you are not in charge anymore maybe you can put this plugin in adoption phase.