Kubernetes: Update SLO resource's status

[metalmatze]

So far running kubectl get slo would only show something similar to this:

NAMESPACE    NAME                                                      AGE
monitoring   servicelevelobjective.pyrra.dev/pyrra-filesystem-errors   18h
monitoring   servicelevelobjective.pyrra.dev/thanos-query              18h

With these changes the status contains the resource type that was generated. Either PrometheusRule or ConfigMap. Additionally, some fields from the spec are extracted and shown in the output too:

kubectl get slo,prometheusrule

NAMESPACE    NAME                                                      WINDOW   TARGET   TYPE            AGE
monitoring   servicelevelobjective.pyrra.dev/pyrra-filesystem-errors   1w       99       PrometheusRule  18h
monitoring   servicelevelobjective.pyrra.dev/thanos-query              4w       99       PrometheusRule  18h

NAMESPACE    NAME                                                           AGE
monitoring   prometheusrule.monitoring.coreos.com/pyrra-filesystem-errors   18h
monitoring   prometheusrule.monitoring.coreos.com/thanos-query              18h

Closes #790 partially