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 adds additional endpoints to the REST API to access the
project relations, the portfolios and topologies that belong to a
project.

This change adds support for restricting API scopes in the OpenDC API
server. This is necessary to make a distinction between runners and
regular users.

This change adds an API endpoint for simulation jobs which allows API
consumers to manage simulation jobs without needing direct database
access that is currently needed for the web runner.

This change addresses some issues in the OpenAPI schema for the
datacenter topology.

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 the Socket.IO endpoint from the public API now that
we have switched to the REST API instead. This decreases the possible
exposure to vulnerabilities as well as the maintenance burden.

This change updates the project structure to become flattened.
Previously, the simulator, frontend and API each lived into their own
directory.

With this change, all modules of the project live in the top-level
directory of the repository. This should improve discoverability of
modules of the project.