switch to use sport=rugby with subtags instead of values rugby_union/rugby_league

[tyrasd]

follow up from #812:

https://wiki.openstreetmap.org/wiki/Tag:sport%3Drugby says that

[…] a consensus has since emerged. It is advised to solely use the primary tag sport=rugby. From there, if you know the version of rugby played at the location you are mapping, you can add a minor tag of rugby=union or rugby=league.

Although no source for where exactly this consensus was found is given (I assume it was a discussion on the talk mailing list), the sport=rugby approach does seem reasonable to me.

However, the wiki is not consistent on this: The Key:sport page does not list sport=rugby at all and the Tag:sport=rugby_* subpages do only slightly hint towards the sport=rugby tag and not list the values themselves as discouraged or deprecated. Further, usage numbers of the "old" tags do not seem to slow down. :thinking:

Checklist:

• [ ] drop the rugby_union value in the sport field
• [ ] add the value rugby in the sport field
• [ ] update the tags of the preset for Rugby League Field
• [ ] update the tags of the preset for Rugby Union Field
• [ ] add deprecation rules for sport=rugby_league to sport=rugby + rugby=league and for sport=rugby_union to sport=rugby + rugby=union

[matkoniecz]

claim seem to be coming from https://wiki.openstreetmap.org/w/index.php?title=Tag:sport%3Drugby&diff=1933218&oldid=1932250