add caddy config

[paulwalko]

Description

Add caddy configuration for reference

I had been using this config for quite a while using the Dockerfile at https://docs.qgis.org/3.34/en/docs/server_manual/containerized_deployment.html with no issue.

I have verified this works following the url structure https://example.com/qgis_mapserv.fcgi?SERVICE=WMTS&REQUEST=GetCapabilities&MAP=/io/data/test/test.qgz with the ltr tag.