fix: add gain for cpxb

[ozym]

This adds a gain override for CPXB, which appears to have had it's continuous digitiser switched from 100 milli-g to 1 mico-g in 2015

Using triggered data compared to the BNZ channel of location: 21 (there will be slight differences as it's going from 200Hz triggered to 50Hz continuous).

Trigger Time	True m/s/s	Corrected m/s/s	Ratio (should be 1.0)
2015-04-05T04:08:31Z	1.973157	0.197006	0.1
2015-04-22T04:52:03Z	1.732325	0.173087	0.1
2015-04-29T00:39:09Z	1.767413	0.177079	0.1
2015-05-17T00:02:01Z	1.724146	1.721332	1.0
2015-05-25T15:17:25Z	1.725951	1.723136	1.0
2015-05-28T22:45:31Z	1.725735	1.719724	1.0

Examining the recorded BNZ data for this stream:

   Source                Start sample             End sample        Hz  Samples
NZ_CPXB_21_BNZ    2015,119,00:00:05.805000 2015,127,01:49:45.105000 50  34888966
NZ_CPXB_21_BNZ    2015,127,02:10:07.840000 2015,138,00:00:05.520000 50  47129885
Total: 1 trace(s) with 2 segment(s)

Provides an estimate of the switch-over time, e.g. 2015,127,02:00:00Z or 2015-05-07T02:00:00Z

The gain of the streams should be reduced by 10.0 prior to this time.

[elidana]

hi @mnaguit , can you please have a look at this pr when you have time? thanks!!

[mnaguit]

Thank you @ozym for these changes. I'll check a couple of events between 2010 to 2015 after the merge and use the main ticket for updates. 👍