package/redis: Install /etc/redis.conf to target

Copy redis.conf from the redis release package but adjust some values to
sensible defaults using 0003-redis.conf-sane-defaults.patch

The file 0003-redis.conf-sane-defaults.patch originates from the redis
package in Arch Linux.

Signed-off-by: Martin Bark <martin@barkynet.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>