Add ability to get a subset of layers using pmtiles extract

[eyeseast]

If I'm using pmtiles extract to get a piece of a larger tileset, sometimes I might not want every layer available. Could extract also filter layers or give me a way to include or exclude layers?

The API could look something like this:

# only extract buildings and county boundaries
pmtiles extract input.pmtiles output.pmtiles --bbox "..." --layers "buildings,boundaries_country"

# get everything except water
pmtiles extract input.pmtiles output.pmtiles --bbox "..." --exclude-layers "water"

[daniel-j-h]

I ran into similar use cases where I started out with the .pmtiles matching the default basemaps style https://github.com/protomaps/basemaps but then wanted to slightly deviate from it. For example when you want a very simple overview map as shown below where we only need to style the water, earth, boundaries layers. At the moment I simply use the .pmtiles with much more data in them as needed by the simple style.

Two more considerations here

• In theory it should be possible to e.g. use ogr2ogr to convert to mbtiles and do the filtering there. In practice only most recent gdal-bin packages contain the pmtiles reader, tho.
• One question could be: should this layer filter be a command line flag for the extract sub-command or should there be a pmtiles filter sub-command, or maybe both?