cassandra: expose the log directory to the pods

Related to T4373

proxmox/terraform/production/cassandra.tf

@@ -23,6 +23,7 @@ resource "rancher2_cluster" "production_cassandra" {
           "/srv/prometheus:/srv/prometheus", # prometheus datastore on mngmt nodes
           "/srv/cassandra_commitlog:/srv/cassandra_commitlog", # writeintensive disks
           "/srv/cassandra_data:/srv/cassandra_data", # mixeduse disks
+          "/srv/cassandra_logs:/srv/cassandra_logs", # mixeduse disks
         ]
       }
     }

[Phabricator Migration user]

Some references in the commit message have been migrated:

• T4373 is now infra/sysadm-environment#4373