Nomad config formalization

We need to formalize our noamd.yaml file structure with a proper datamodel and versioning. The best approach might be to define it as a pydantic model wit h proper descriptions, validation, (de)serialization etc.

This should be started with a first version that:

• Define a basic pydantic model with descriptions and data types, no complex validation yet
• Add the possibility to create a markdown document from the model that can be put into our docs.
• Recreate the existing functionality: defaults->config file->env variables->derived values
• Add a separate version number to the config model. This will allows us to perform migrations and checks when people use different config versions.