[snmp] Upgrades and enhancements (#14330)

* [snmp] Upgrades and enhancements

- bug: improve test stability
- enhancement: add support for UoM
- bug: fix misleading error message
- bug: fix initialization exceptions
- enhancement: Add support for SNMPv3
- enhancement: add opaque value handling

Signed-off-by: Jan N. Klug <github@klug.nrw>

CODEOWNERS

@@ -308,7 +308,7 @@
 /bundles/org.openhab.binding.smhi/ @pacive
 /bundles/org.openhab.binding.smsmodem/ @dalgwen
 /bundles/org.openhab.binding.sncf/ @clinique
-/bundles/org.openhab.binding.snmp/ @openhab/add-ons-maintainers
+/bundles/org.openhab.binding.snmp/ @J-N-K
 /bundles/org.openhab.binding.solaredge/ @alexf2015
 /bundles/org.openhab.binding.solarlog/ @johannrichard
 /bundles/org.openhab.binding.solarmax/ @jamietownsend