Validate benchmark manifest in the controller

Today invalid configuration show random exceptions in the code base. Once that succeeds, it's possible to have an invalid configuration model and we don't have much validation in place today (besides very basic required fields, like the name of services).

We need to do both input validation and model validation:

Input validation - Making sure the configuration schema is correct (type checking).
Model validation - Making sure the configuration is valid after it is correctly parsed.