Add warning about breaking change for maps

[LiamConnors]

Add warning about breaking change for maps: 'country names' locationmode option

See plotly/plotly.js#7514 for details on the warning in Plotly.js

[LiamConnors]

@gvwilson I think this should be added to the code as a warning like we did for the mapbox to maplibre changes (#4900) instead of just to the docs
might need some codegen updates
cc @emilykl @camdecoster

[gvwilson]

cc @daexs

[emilykl]

@gvwilson @LiamConnors This is done, see #5318. Let me know if it's not showing up properly for you.