[Visual Refresh][Maps] Update EMS styles to Borealis

[nickofthyme]

With the new Borealis theme being added in #199993 we need to update the styles of the maps visusalization.

To view the current styles you can use Maputnik app and use the Load from URL option by pointing to the raw files on github.

Maps on Borealis Light mode

Light styles stored here

Maps on Borealis Dark mode

Dark styles stored here

cc: @gvnmagni @JasonStoltz

[elasticmachine]

Pinging @elastic/eui-team (EUI)

[elasticmachine]

Pinging @elastic/kibana-presentation (Team:Presentation)

[jsanz]

Thanks @nickofthyme for opening this issue 🙇

I'd like to put some time on thinking if the new styles could be implemented as some set of controlled changes we can put on top of our current styles to keep everything easier to maintain in the future with new releases of the OpenMapTiles schema or just go ahead and fork these new styles from our current ones.

@gvnmagni any advice on the minimum changes you'd like to see on the new styles to adapt to the Borealis theme would be appreciated! So for example for the light theme maybe a brighter gray for the sea background would be nice and a general more blueish tint to the dark theme would be a minimum but maybe there's room for more significant changes?

Sharing here a small experiment using the tinting feature in Kibana Maps basemap properties to get an idea of the effect of applying an overall color correction to our dark style.

Finally, our Tile Service is not versioned and we deploy a single basemap dataset so we will need to add new styles while maintaining the current ones for our pre-Borealis users, so we need to also put some work in our backend to create these two new styles. Issues and PRs related to that will backlink to this issue to keep track of them.

[gvnmagni]

Thank you both for starting the conversation, I have been waiting for the first release by EUI to do a proper walkthrough and take some notes about this.

If you are ok, my plan for next week is to do it and list a series of fixes that could be done very quickly to align the visual style of maps to the new theme. I don't expect this to be bigger than a few swaps of color variables.

Then, I would love to talk with you Jorge (and maybe the rest of the presentation Team + Nick + EUI people maybe) to see if it is necessary to consider bigger changes. I don't think that's going to be the case, I just want to be sure that the Presentation Team is introduced to the new tokens structure and its mechanism and we are all aligned.