Minor updates to redis setup.

[cfi-gb]

This is a follow-up of https://github.com/Atomicorp/openvas-docker/commit/18065fe4fd2b924bba0a1b5468b38e537c85d8cc:

• Commenting out the bind part just made redis to listen on all interfaces like explained one line above, not to only listen on a unix socket
• Setting port 0 so listening on a TCP socket is skipped
• Moving the socket stuff to the part where the description is located
• Raise the databases to match whats suggested in https://wald.intevation.org/scm/viewvc.php/trunk/openvas-scanner/doc/example_redis_2_6.conf.in?root=openvas&view=markup
• Explain why the save statements are commented out
• Add the path to the redis-cli command which needs to point to the socket after the changes above