Adjust NodeClock* alerting rules to be inactive when the PTP operator is installed

When the PTP operator is installed, it brings its own alerting rule to detect clock drift which is more reliable than the out-of-the-box NodeClockNotSynchronising and NodeClockSkewDetected alerts:

https://github.com/openshift/ptp-operator/blob/4845b7ce41f44e8e62c1a66f6a41afd400b0e466/bindata/linuxptp/ptp-daemon.yaml#L222-L255

The NodeClockNotSynchronising PromQL expression should be adjusted to "mute" itself when the PTP operator is installed.

expr: |
(
        min_over_time(node_timex_sync_status{job="node-exporter"}[5m]) == 0
        and
        node_timex_maxerror_seconds{job="node-exporter"} >= 16
)
 # addition to the upstream expression
and on() absent(up\{job="ptp-monitor-service"})