[performance] Improve legend rendering

[markov00]

Long legends are rendered without considering the number of elements that can be too much to be represented and can just waste rendering time.

We can consider a windowing/virtualized function to render legend lists with more than 50/100 items. Hopefully without the need to introduce a third party library.

Double check if the EBT journeys have charts with a lot of elements to see if this improvements can actually impact the journeys metrics or not