Use config directory to separate configuration files for Hugo
We should separate the config.toml file into smaller files like we do on jakarta.ee.
As the repository grows, and the number of sections grow, we need a better way to organize things like menus. We also have sections like /research which will have their own menus. See eclipsefdn/it/webdev/hugo-solstice-theme#265 (closed).
/cc @pkriefrvi