Use updated squid image from ghcr.io

Remove dependency on docker.io, because pulls can be rate-limited.
Pull squid from ghcr.io, and update to a modern version based on
rockylinux 10 and squid 6.10.

Author: m-bull

etc/kayobe/seed.yml

@@ -127,9 +127,9 @@ seed_squid_container_enabled: false
 
 seed_squid_container:
   squid:
-    image: docker.io/stackhpc/squid
+    image: ghcr.io/stackhpc/docker-squid
     pre: "{{ kayobe_config_path }}/containers/squid_proxy/pre.yml"
-    tag: "4.15"
+    tag: "6.10"
     network_mode: host
     volumes:
       - squid_spool:/var/spool/squid