Order manifest fields based on `order` value

[camdendotlol]

The metadata fields in the manifest should be sorted based on the order configured in the model settings.

see performant-software/libertos-content#8

[ajolipa]

Testing notes

Specify the order of user defined fields on a media_contents model and then update a record; in the displayed IIIF viewer metadata tab the fields should appear in the configured order.

[blms]

@camdendotlol @ajolipa This works, but I guess (because it has to trigger manifest regeneration?) reordering fields in a model with lots of existing records would then require updating every single record by hand.

Maybe that's an unusual scenario, but I could see it being confusing if some records appear to get the correct order and some don't. I wonder if, when a media contents model changes, we ought to check if UDFs were reordered, and if so, queue regeneration of all manifests? (not sure if that would be a huge bottleneck on the IIIF server…)

That said, if this meets the client's requirements then it's probably good enough for now

[camdendotlol]

Yes, that occurred to me when working on the feature but I wasn't sure if it was feasible to queue up potentially thousands of manifest jobs. I guess we're doing something similar during the import process, so maybe it would be fine?

[blms]

@camdendotlol If it could work the same as during import, then I'd support it. I'll leave it to your / PM discretion as to the client's needs though.

[camdendotlol]

I think it's fine as-is for Libertos. They won't have many media records. We should probably file an issue though.

[blms]

That sounds good!