feat: receive and use tags in image options

[krynju]

Image options are being extended by tag and sha.
Previously an image option would be an image key and a type.

Now optionally an image_tag or image_sha field can appear in the image option and they should be used in job submission if chosen.
The other bigger change is that the unique constraint on options is no longer just the key, but now it's a unique constraint on key, tag and sha. This means the same key can appear multiple times with different tag/sha combinations.

This should be nonbreaking in any direction. Older client ignores the tag/sha and will just list another option with the same key. Older instances will never send tag/sha so using a newer client there is ok too.