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.

This change removes the event tracer from the OpenDC Workflow service as
we start migrating to the industry standard OpenTelemetry.

This change integrates the OpenTelemetry Metrics API in the OpenDC
Workflow Service implementation. This replaces the old infrastructure for
gathering metrics.