Feature request: SNMPv3 support

[jeremmfr]

By @AndriiPysmenko in #337 :

Add SNMPv3 support to junos_snmp resource:

set snmp view all oid .1 include
set snmp engine-id use-mac-address
set snmp v3 usm local-engine user test_read authentication-md5 authentication-password PASSWORD
set snmp v3 usm local-engine user test_read privacy-none
set snmp v3 vacm security-to-group security-model usm security-name test_read group test_read
set snmp v3 vacm access group test_read default-context-prefix security-model usm security-level authentication read-view all
set snmp v3 usm local-engine user test_write authentication-md5 authentication-password PASSWORD
set snmp v3 usm local-engine user test_write privacy-none
set snmp v3 vacm security-to-group security-model usm security-name test_write group test_write
set snmp v3 vacm access group test_write default-context-prefix security-model usm security-level authentication read-view all
set snmp v3 vacm access group test_write default-context-prefix security-model usm security-level authentication notify-view all
set snmp v3 vacm access group test_write default-context-prefix security-model usm security-level authentication write-view all

[jeremmfr]

I will take care of adding this.