This change removes the dependency on the OpenTelemetry SDK. Instead,
we'll only expose metrics via the OpenTelemetry API in the future via
adapter classes.

This change updates the Gradle build configuration of the project to
publish the different type of modules (e.g., opendc-compute,
opendc-simulator) into their own groups.

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.