nixos/modules: fix systemd start rate-limits

These were broken since 2016:
https://github.com/systemd/systemd/commit/f0367da7d1a61ad698a55d17b5c28ddce0dc265a
since StartLimitIntervalSec got moved into [Unit] from [Service].
StartLimitBurst has also been moved accordingly, so let's fix that one
too.

NixOS systems have been producing logs such as:
/nix/store/wf98r55aszi1bkmln1lvdbp7znsfr70i-unit-caddy.service/caddy.service:31:
Unknown key name 'StartLimitIntervalSec' in section 'Service', ignoring.

I have also removed some unnecessary duplication in units disabling
rate limiting since setting either interval or burst to zero disables it
(https://github.com/systemd/systemd/blob/ad16158c10dfc3258831a9ff2f1a988214f51653/src/basic/ratelimit.c#L16)

nixos/modules/services/network-filesystems/ceph.nix

@@ -28,6 +28,9 @@ let
 
     # Don't start services that are not yet initialized
     unitConfig.ConditionPathExists = "/var/lib/${stateDirectory}/keyring";
+    startLimitBurst =
+      if daemonType == "osd" then 30 else if lib.elem daemonType ["mgr" "mds"] then 3 else 5;
+    startLimitIntervalSec = 60 * 30;  # 30 mins
 
     serviceConfig = {
       LimitNOFILE = 1048576;
@@ -39,8 +42,6 @@ let
       ProtectHome = "true";
       ProtectSystem = "full";
       Restart = "on-failure";
-      StartLimitBurst = "5";
-      StartLimitInterval = "30min";
       StateDirectory = stateDirectory;
       User = "ceph";
       Group = if daemonType == "osd" then "disk" else "ceph";
@@ -48,13 +49,10 @@ let
                     -f --cluster ${clusterName} --id ${daemonId}'';
     } // optionalAttrs (daemonType == "osd") {
       ExecStartPre = ''${ceph.lib}/libexec/ceph/ceph-osd-prestart.sh --id ${daemonId} --cluster ${clusterName}'';
-      StartLimitBurst = "30";
       RestartSec = "20s";
       PrivateDevices = "no"; # osd needs disk access
     } // optionalAttrs ( daemonType == "mon") {
       RestartSec = "10";
-    } // optionalAttrs (lib.elem daemonType ["mgr" "mds"]) {
-      StartLimitBurst = "3";
     };
   });