feat: Switch to endpoint-mode dnsrr instead of vip

The default docker swarm endpoint mode (vip) introduces unnecessary
indirection in the communication between services, namely the
docker-proxy and a dynamic haproxy endpoint container. This commit
switches the socket-proxy service to endpoint_mode: dnsrr by default and
the traefik service when using host-mode port publishing.

I would strongly recommend considering switching to host-mode port
publishing by default, especially as most coop-cloud deployments are
single-server.

See: toolshed/organising#648

Thanks to @mirsal. Rebased and merged from the following commit.
abbb3255f8

compose.yml

@@ -53,6 +53,8 @@ services:
 
   socket-proxy:
     image: lscr.io/linuxserver/socket-proxy:1.26.2-r0-ls30
+    deploy:
+      endpoint_mode: dnsrr
     environment:
       - ALLOW_START=0
       - ALLOW_STOP=0