Replace Lutok with another widely adopted upstream config file format, e.g., TOML

[ngie-eign]

Lutok, as it stands, exists purely to provide a C++ interface to Lua for Kyua so Kyua can define test metadata in Kyuafiles using the Lua programming language.
Lutok was developed over a decade ago (2014) as part of Kyua. Over the past decade, the configuration file landscape has grossly changed. Other formats like TOML and YAML have emerged and been widely adopted by a variety of projects.
In order to shed some maintenance cost associated with Lutok, etc, I think it's a good idea to move Kyua to another config file format and sunset the Lutok project.