Support configurable exif tags for image logging

[richard-rogers]

Description

Adds ImageMetricConfig <: MetricConfig that allows you to specify exif tags to track.

Changes

[jamie256]

I'm not sure I understand the scenario this is targeting. Can you show what happens with input images that already contain exif tags (what happens without your changes and what does this change provide)?

Thanks for the offline explanation, what I was missing is that there is a limitation in the current compound metrics in that they resolve the set of submetrics once when initialized, hence the dummy image log in zero(). In v0 the exif tags were logged as columns which can be dynamically added to a dataset profile after logging has started.

We should see if we can support dynamically adding submetrics to compound metrics after initialization so that we don't need to configure the set of submetrics before logging. This will take some rework of compound metrics but should simplify what a caller has to configure before logging images.

[richard-rogers]

Solved this in a different PR