Set power policy to always turn on

In all machines, as soon as we recover the power, turn the machine back
on. We cannot rely on the previous state as we will shut them down
before the power is cut to prevent damage on the power supply
monitoring circuit.

m/module/power-policy.nix

@@ -8,7 +8,7 @@ in
 {
   options = {
     power.policy = mkOption {
-      type = lib.types.nullOr (types.enum [ "always-on" "previous" "always-off" ]);
+      type = types.nullOr (types.enum [ "always-on" "previous" "always-off" ]);
       default = null;
       description = "Set power policy to use via IPMI.";
     };
@@ -23,6 +23,8 @@ in
         Type = "oneshot";
         Restart = "on-failure";
         RestartSec = "5s";
+        StartLimitBurst = "10";
+        StartLimitIntervalSec = "10m";
       };
     };
   };