Adding action id prop

Signed-off-by: Tihomir Surdilovic <tihomir@temporal.io>

Author: tsurdilo

api/src/main/resources/schema/actions/action.json

@@ -3,6 +3,10 @@
   "javaType": "io.serverlessworkflow.api.actions.Action",
   "description": "Action Definition",
   "properties": {
+    "id": {
+      "type": "string",
+      "description": "Unique action identifier"
+    },
     "name": {
       "type": "string",
       "description": "Unique action definition name"