Unify colour & display name setting for all models

[jameshadfield]

Over time setting the clade colours & display names separately to the lineage colour definitions resulted in the two falling out of sync. This work unifies the approach so that the same script (using a unified configuration) modifies each JSON respectively.

Including the colour and display name data within the clades JSON is a big improvement as it allows simple retrospective analysis of old datasets.

Tested locally with no observed changes to the resulting colours.

[trvrb]

Another observation (that I don't know where to thread really)... if I take the resulting file 2023-10-24_results.json and drag-n-drop to https://nextstrain.github.io/forecasts-viz/ the resulting display is the generic color ramp rather than the hex values encoded in the JSON.

[jameshadfield]

I've updated this PR to generate colour ranges from the provided clade colour (see commentary in the code of that function - I don't think the colours are better than using cmaps, but they are certainly much easier to maintain!) and also shifted the clade definitions into the config.

Another observation (that I don't know where to thread really)... if I take the resulting file 2023-10-24_results.json and drag-n-drop to https://nextstrain.github.io/forecasts-viz/ the resulting display is the generic color ramp rather than the hex values encoded in the JSON.

Oh! How annoying. ~The viz app must not be up-to-date. I'll update it.~ I've updated the viz app and it's now working.

[jameshadfield]

I'm going to merge this now - any colour fixes (etc) can be easily applied by subsequent PRs if needed.

[trvrb]

Thanks so much for the changes here James (and sorry that I forget to follow up). I really appreciate this. It should make things much more maintainable going forward.