improve reporting of offset between NTP and WR time

Currently, the difference between NTP and WR is reported in by SNMP in "wrsSystemClockDrift" in seconds. It would be very useful to have this value reported in miliseconds, are just directly from the daemon as fractional value. The data reported by the daemon:

ctdwa-354-cttmaster1#/usr/sbin/ntpd -n -w -q -d -p ip-time-4.cern.ch
ntpd: sending query to 172.18.17.69
ntpd: reply from 172.18.17.69: offset:-0.492925 delay:0.002000 status:0x24 strat:1 refid:0x00535047 rootdelay:0.000000 reach:0x01

Likely, add a new OID wrsSystemClockDriftRaw or something

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