Improve Marker performance

[Zottelchen]

(Not entirely sure if this counts as bug or feature request.)

What i did / Steps to reproduce

1. I rendered a map
2. I added a whole lot of markers (~8MB marker file)
3. I opened the map

Expected result

I can use a lot of markers smoothly. (This was not an issue with leaflet maps, but Bluemaps is admittedly cooler :))

Actual result

Everything is slow. See for yourself https://map.drehmal.cyou/

Context

BlueMap Version: Docker/CLI: ghcr.io/bluemap-minecraft/bluemap:latest (Should be 5.3, webpage says 5.2 though)

[TBlueF]

I will definitely consider marker-performance with the webapp-rewrite that i want to do and #244.

Duplicate of #558
Closing because of this :)