Loki: Move chunks and rules into separate folders

[root@monitoring:~]# ls -l /var/lib/loki | wc -l says "3358" because new Loki is by default saving everything into the same directory (meh!)

nixos/modules/monitoring/server/loki.nix

@@ -30,6 +30,12 @@ in {
           instance_addr = "127.0.0.1";
           replication_factor = 1;
           path_prefix = "/var/lib/loki";
+          storage = {
+            filesystem = {
+              chunks_directory = "/var/lib/loki/chunks";
+              rules_directory = "/var/lib/loki/rules";
+            };
+          };
         };
 
         server = {