feat(bot-detection) per-worker cache UA lookups
feat(bot-detection) per-worker cache UA lookups

Bring back the old behavior of caching UA lookups per-worker in
the bot detection plugin. This behavior was removed during serf
removal. A local table is used to cache lookup results of the UA
based on the plugin config; this cache is purged when the plugin
is updated.

Kong/kong,jebenexer/kong,icyxp/kong,salazar/kong,shiprabehera/kong,Mashape/kong,Kong/kong,Kong/kong