Updating the promethes reources (PrometheusRule and ServiceMonitor) is
done by fetching the current resource from the server and updating the
spec on it. This commit makes it also apply the labels, so users can
update them via rook CRDs.
Closes: https://github.com/rook/rook/issues/9241
Signed-off-by: Mara Sophie Grosch <littlefox@lf-net.org>