Feature: Terrain Preview and simple Elevation Query

[okimiko]

This PR will add

• a preview for terrain data (in addition to the current raw data preview)
  • highlight color is based on the encoding
• a simple elevation api based on served terrain data
  • includes a link on the index page
  • for details, see endpoints.rst

Both require configured encoding (see config.rst).

In general this adds just some eye candy and an "inspect" function for terrain like the geojson endpoint.

[acalcutt]

we are going to need to find a good spot to put this documentation since it doesn't just apply to mbtiles. maybe a new section that notes this and the information right below. ir might be good to note it only works with pmtiles or mbtiles

[okimiko]

I would like the second approach, in general the tileserver handles "data" even if we add some special terrain handling here, I think there is no need to show that in an own section. (This may change, if there will be more features in this section ;-)).

[okimiko]

I miss understood your comment (I read it as a change of the code regarding configuration).

I updated the documentation with a dedicated section nested in "data".

[okimiko]

Thanks for all suggestions so far. I did a local build and converted my terrain mbtile source to a pmtile and both are working so far :)