rgw: RGWPubSub requires SiteConfig

rgw: RGWPubSub requires SiteConfig

RGWPubSub constructor takes SiteConfig instead of zonegroup map

replace do_all_zonegroups_support_notification_v2() with a generic
function rgw::all_zonegroups_support() that handles non-realm
configurations too

remove unused sal::ZoneGroup::supports_feature()

Signed-off-by: Casey Bodley <cbodley@redhat.com>
(cherry picked from commit 1fccdad21d5bcdebbdd7167b7ed18391a1e8d1e2)