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

This change removes the dependency on the event tracer in
`opendc-trace`, since we are in the process of migrating OpenDC to
use OpenTelemetry for distributed tracing and metrics.

This change adds a test suite for the OpenDC compute service.

This change introduces the ComputeService interface (previously
VirtProvisioningService) and provides a central implementation in
opendc-compute-service.

Previously, the implementation of this interface was bound to the
simulator package, which meant that independent business logic could not
be re-used without importing the simulator code.