Better seperation of layer definitions and deployment information

[pnorman]

I'm writing layer definitions I'd like others to be able to use, but the config files are a mix of layer definitions (tileset stuff) and deployment information like IP addresses ([webserver] stuff). It would be good to have these independent so I can distribute layer definitions without making too many assumptions about someone's configuration.

[pka]

Makes sense to me. What about an option configdir which holds partial TOML configurations?

[fracaron]

Something like include = ["datasource1.toml, layer1.toml, layer2.toml] would be very useful in term of readability and reusability for complex configuration.

[pka]

With the new template support, the configuration can be split into mutlple files and variables can be passed via environment variables or in a .env file.