Add missing mod_socache_redis.xml file

It was part of http://home.apache.org/~jim/patches/socache_redisv2.patch but is not in r1855817.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1856454 13f79535-47bb-0310-9956-ffa450edef68