This change adds the initial implementation of the new API server in Kotlin,
replacing the old API written in Python. The implementation uses Quarkus,
RESTEasy, and Hibernate to implement the new API endpoints.

The reason for replacing the old API server is unifying the build and
deployment toolchains, reducing the number of technologies necessary to
work with OpenDC. Furthermore, we envision bundling the entire OpenDC
project into a single distributions, allowing users to launch their own
deployment trivially.

This change updates the API Schema to the more recent OpenAPI version 3
and in addition actualizes the API specification to match the API
again.

This change adds Swagger UI to the REST API endpoint in order to
experiment with the API endpoints interactively. It also serves as the
documentation for the API endpoints.

This change removes any of the user handling and endpoints from the
OpenDC API server. The API server does not need to store user
information other than an identifier in the database.

This change reformats the API spec to follow the YAML spec and the
updated EditorConfig.

This change adds a bridge between the frontend and the new simulator
implementation via MongoDB.