Retain platformio cache

As compiling might take long, it is not a good idea to remove the
platformio cache with the `rsync --delete` on every deployment.

hosts/iron/services/esphome/default.nix

@@ -43,9 +43,21 @@ in
   system.activationScripts.esphome-custom = {
     deps = [ "users" "groups" ];
     text = ''
-      mkdir -p "${stateDir}/.esphome"
-      ${pkgs.rsync}/bin/rsync -a --delete "${cfgdir}/" "${stateDir}/"
-      chown esphome:esphome "${stateDir}/"
+      ${pkgs.rsync}/bin/rsync \
+        -a \
+        --delete \
+        --exclude=.esphome \
+        --exclude=.platformio \
+        --exclude=.gitignore \
+        "${cfgdir}/" "${stateDir}/"
+      mkdir -p \
+        "${stateDir}/.esphome" \
+        "${stateDir}/.platformio"
+      touch "${stateDir}/.gitignore"
+      chown esphome:esphome \
+        "${stateDir}/" \
+        "${stateDir}/.esphome" \
+        "${stateDir}/.platformio"
     '';
   };
 }