This change removes the opendc-platform module from the project. This
module represented a Java platform which was previously used for sharing
a set of dependency versions between subprojects. However, with the
version catalogue that was added by Gradle, we currently do not use the
platform anymore.

This change updates the build configuration to also publish the Java
Platform on Maven Central. This is necessary since the other modules
depend on the platform.

This change adds support for the Gradle version catalog feature in our
build configuration. This allows us to have a single file,
gradle/libs.versions.toml, which contains all the dependency versions
used in this project.

This change adds support for configuring the experiments via
configuration files using the TypeSafe config library. In the future, we
will also integrate support for configuration into the harness.

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.