ApiQuerySiteinfo: Add prop=restrictions for protection information

ApiQuerySiteinfo: Add prop=restrictions for protection information

As pointed out on VPT, we previously had no way to find out about these.

This just dumps the raw config variables for now. They are documented
in DefaultSettings as having some magic applied to them when used,
maybe we should apply this magic here too, or in Setup.php?

https://en.wikipedia.org/w/index.php?title=Wikipedia:Village_pump_(technical)&oldid=594218538#API_query_to_list_available_protection_levels_for_a_wiki.3F

Change-Id: I4c1303f2a6fe6b60b44e960cc1253c555fc658dc