Write model code using OpenSLO JSON-Schema Def

[CRThaze]

Once you have a common package in place you can start adding your own entity definitions. For the exact details on how to do that we defer to getting inspired by the existing scaffolder-common package. But in short you will need to declare a TypeScript type and a JSONSchema for the new entity kind.

Since the JSONSchema is not yet published to the web, we should probably use a git-submodule for the schema definition until that gets finished.