Convert OS mrv-od to yaml, discover more sensors, discover entity-physical (#10266)

* Dynamic entPhysicalIndex values for YamlDiscovery

* Use degree symbol when displaying temperature values

* Adjust SNMP options for new snmp_get_multi()

The OS polling module for mrv-od was using snmpget commands with
-Ovqs, rather than -OQUs, which meant that the equal sign was
stripped in the snmpget output. But that equal sign is now used
as the explode() delimiter so it broke the construction of the
returned array for the snmp_get_multi() function.

Additionally, I removed the NBS-CMMC-MIB:: prefix which is no
longer returned by snmp_get_multi() as part of the OID. Now,
the mrv-od.inc.php OS polling module is retrieving data from
positions in the array with actual content.

* Convert mrv-od to yaml, improve sensors discovery

Converted sensors discovery for mrv-od to yaml, retaining all
functionality for pre-cache, dbm, and temperature. Replaced specific
SFF-8472 Digital Diagnostics state sensors with generic ones, given that
we are now reading out detailed values through new dbm, current, voltage
sensors.

Reasoning: the generic Digital Diagnostics state sensors report state
diagsOk, or else the worst severity level measured among all of the
Digital Diagnostics values for that optical data point. You'd really
only want to set a generic "alarm" so the box can report that it
thinks something is wrong, whereafter a human can look at the graphs
and/or the CLI to draw their conclusions about the alarm. Otherwise,
things would quickly become too spammy as you are essentially duplicating
every sensor across both regular measurements and state measurements.

Further changes:
- Increase maximum number of detected PSUs from 4 to 8 per the MIB.
- State sensor to detect (in)sufficient power budget for all modules.
- Use skip_values to hide state sensors with the notSupported value.
- Use skip_values to hide sensors which are unsupported per the MIB,
  signified by the device returning special values -1 or -2147483648.
- Add dBm, temperature "over" graphs to the mrv-od device header bar.

* Add mrv-od entity-physical support

MRV does not use the ENTITY-MIB data format, so we had to reconstruct
the inventory from their proprietary format using the following tables
from their NBS-CMMC-MIB:

- nbsCmmcChassisTable
- nbsCmmcSlotTable
- nbsCmmcPortTable

Additionally, since sensors didn't have their own ifindex in the
NBS-CMMC-MIB, I went ahead and appended the last OID digit to
the "containing" ifindex create a unique number. The same was
done for the sensors in the yaml-discovery.

* Test data for mrv-od, fix 2* pre-commit.php issues

* Fix entPhysicalIndex returning 0 instead of null

Some unit test breakage was caused by 62167ebcb which changed
the code to return 0 instead of null when {{ $index }} was
set as the entPhysicalIndex in the YamlDiscovery. So now we
detect if it returns some value which may be interpreted as
false, and if so we set null rather than 0.

includes/rewrites.php

@@ -1708,7 +1708,7 @@ function get_units_from_sensor($sensor)
         case 'state':
             return '#';
         case 'temperature':
-            return 'C';
+            return '°C';
         case 'voltage':
             return 'V';
         default: