Implement workflow status for metrics update task

[nscuro]

As part of #664, updating of the workflow status for the METRICS_UPDATE step must be implemented.

Before ComponentMetricsUpdateTask and ProjectMetricsUpdateTask are executed, the tasks must check whether a workflow step of type METRICS_UPDATE exists for the token associated with the event they receive (Event#getChainIdentifier). If so, the startedAt timestamp of that step must be updated accordingly.

Upon completion or failure of the task, the corresponding step's status must transition to either COMPLETED or FAILED respectively. In case of a failure, the failureReason of the step must be populated.

Note that both metrics tasks can be executed outside of a workflow, for example during the scheduled portfolio metrics update. The tasks thus need to be able to work without corresponding workflow step.