Use Statis of CRs instead of a queue inside the Operator

In Kubernetes, resources can have a status, such as PENDING or RUNNING. The operator should use this status instead of a queue to manage the custom resources for execute and benchmark objects.

This means that the operator should set the status of all deployed CRs to PENDING, when an execution is running, the status should be RUNNING and when the execution is finished, the status should be set to FINISHED. If an error occurs, the status should be set to FAILURE and if an execution is interrupted, the status should be set to INTERRUPTED. If an execution is changed, the status should be set back to PENDING. If the operator finds an execution whose status is RUNNINGalthough the operator is not currently executing the execution, it should be restarted (then, the status is set to RESTART). A benchmark should be either PENDING or RUNNING.

This issue relates to #213 (closed) and #190 (closed)