[RFC] Refactor documentation system

[Nek-]

The current documentation system is based on swagger-php, which is a pain. The automatic generation of the documentation is a real pain for the maintainers of Melodiia. Documentation extension process will be a pain for users...

That's why I suggest removing the automatic generation of documentation. Melodiia will just provide swagger integration (a controller that render swagger). This means adding a new configuration item for the documentation file (yaml). We're also gonna remove any documentation item from the configuration.