Allow users to specify label->color mapping

[mistercrunch]

Users can define label_colors in a dashboard's JSON metadata that enforces a label to color mapping.

It's common for user to want certain series to be a specific color ('forecast' should be a blue line, 'actual' is green), or to want consistency across dashboard refreshes (which we don't provide at the moment)

This also makes the function that maps labels to colors case insensitive.

@michellethomas @graceguo-supercat @williaster @john-bodley

BTW it could be nice to allow global settings (apply to all dashboards) for this somewhere.

[fabianmenges]

This is out of scope of this change, but I feel like we should have a UI to do this and not just manually writing json into this metadata field.

Apart from that I find it extremely difficult to find documentation (e.g. why is a very specific dashboard feature mentioned in a FAQ) for these kinds of features, we should probably reorganize our docs by functionality. Have a single doc for all the things you can specify on dashboard.

[mistercrunch]

Totally agree about the docs, I think about this every time I add an FAQ entry. It's just always out-of-scope for the particular thing I work on to reorg the docs. Let's talk about this item briefly at the meeting tomorrow.

[mistercrunch]

Also agree about having this in the UI and that's true of most of the things in "Metadata JSON".

I think it's a good pattern to have a way to add features for power users that are scaffolding for future UX components. This allows us to roll out key features with a fraction of the dev time, and we can always finish up the work later based on usage/popularity. This is especially good for uncommon-but-required features.

I wonder if there was a halfway between free-form JSON, and the UX features, say a little JSON editor that forces certain shapes and types.

[mistercrunch]

Waiting for #3887 to rebase against

[williaster]

@mistercrunch @fabianmenges we have been discussing adding global time + global color controls to dashboards in our dashboard re-design talks, can discuss more tomorrow?

If we're going to do a decent amount of work on the dashboards I don't think we should have a partial UI for it, we should just do it properly :) this is great for the logic component.