Add config file validation step to CI tasks list

[atc0005]

Example:

config.example.toml file for atc0005/dnsc project was modified in atc0005/dnsc#40 and the CI run declared "no conflicts". If I had introduced a typo, I'd like for that to fail the build.

Goals:

• validation for TOML files
• validation for YAML files (likely to start using this soon)
• validation for JSON files

[atc0005]

Goals:

• validation for TOML files

https://github.com/pelletier/go-toml#tools

Go-toml provides two handy command line tools:

tomll: Reads TOML files and lint them.

go install github.com/pelletier/go-toml/cmd/tomll
tomll --help