Improve Metric compliant status

[lebogg]

When investigating the assessment results (go to "Assessment" in UI), hovering over the Compliant symbol (first column), the message can be very meaningless, e.g.:

1. "Resource is not compliant: Metric was not == true
2. "Resource is not compliant: Metric was not >= [object Object], [object Object], [object Object], should be false"

While the first example got also tackled by providing a metric name and description for all metrics (see clouditor/clouditor#881), the second one likely remains quite meaningless.