Update haproxy config to use port 6379 for redis

[dmc5179]

The haproxy config for deploying Quay in HA mode has redis on port 6380 in the backend while the redis deployment steps have redis on port 6379 here:

# mkdir -p /var/lib/redis
# chmod 777 /var/lib/redis
# sudo podman run -d -p 6379:6379 \
    -v /var/lib/redis:/var/lib/redis/data:Z \
    registry.redhat.io/rhel8/redis-5

This PR aligns the haproxy config in the documentation with the redis deployment steps as well as the testing resource haproxy config and ansible deployment file.