[FEATURE] Have a central download folder like `~/.planetiler`

[wipfli]

Is your feature request related to a problem? Please describe.

I am always a bit frustrated when I want to make a new nice planetiler map in a different folder, but then I first need to wait until all the big natural earth data is downloaded into the local data/ folder...

Describe the solution you'd like

Save all natural earth and geofabrik data in a central location, like for example in ~/.planetiler.

Describe alternatives you've considered
Always build your planetiler maps from the same folder, but this is a bit of a mess for me because I am used a folder or github repo per idea...

Additional context
Planetiler is great!