Add new example template for scanning UDP services
Usability improvements to UDPScanner

* Add RPORT as a regular option, define rport
* Add CPORT as an advanced option, define cport
* Change CHOST to an advanced option
* Use a more sane THREADS value since hosts are scanned in batches
More sane % printing for aux scanner
Trailing ,
Improvements to example UDPScanner
More sane % printing for aux scanner
Example per-batch vprint, a useful default
Move default probe and result store to UDPScanner, since most need it
Example UDPScanner style cleanup, move most to UDPScanner
Update .rubocop.yml to use correct Metrics namespace
Disable UnneededPercentQ in Rubocop
update_info
rport, not datastore['RPORT']
Move to build_probe
Add the UDP scanner template, lands #4113.

There is some additional work to do regarding CHOST/CPORT, but this is not tied to the udp template changes.