entity-manager: extract function addObjectJson

extract function `addObjectJson` from `addObject` function.

This separates the data conversion from core `AddObject` logic which
operates on json (as usual with EM internals).

Tested: on Tyan S8030:

Adding a dummy record:

```
root@s8030-bmc-30303035c0c1:~# busctl call xyz.openbmc_project.EntityManager /xyz/openbmc_project/inventory/system/board/Tyan_S8030_Baseboard xyz.openbmc_project.AddObject AddObject a{sv} 3 Name s DummyRecord Type s DummyType PollRate u 1000

root@s8030-bmc-30303035c0c1:~# busctl introspect xyz.openbmc_project.EntityManager /xyz/openbmc_project/inventory/system/board/Tyan_S8030_Baseboard/DummyRecord

NAME                                        TYPE      SIGNATURE RESULT/VALUE  FLAGS
...
xyz.openbmc_project.Configuration.DummyType interface -         -             -
.Delete                                     method    -         -             -
.Name                                       property  s         "DummyRecord" emits-change
.PollRate                                   property  d         1000          emits-change
.Type                                       property  s         "DummyType"   emits-change
```

New record is added without issues.

Change-Id: I62e2276ff517d0369f5644fa21dae162c44590db
Signed-off-by: Alexander Hansen <alexander.hansen@9elements.com>
diff --git a/src/entity_manager/dbus_interface.hpp b/src/entity_manager/dbus_interface.hpp
index 3e24768..1f978bc 100644
--- a/src/entity_manager/dbus_interface.hpp
+++ b/src/entity_manager/dbus_interface.hpp
@@ -55,6 +55,12 @@
         nlohmann::json& systemConfiguration, const std::string& jsonPointerPath,
         const std::string& path, const std::string& board);
 
+    // @brief: same as 'addObject', but operates on json
+    void addObjectJson(nlohmann::json& newData,
+                       nlohmann::json& systemConfiguration,
+                       const std::string& jsonPointerPath,
+                       const std::string& path, const std::string& board);
+
     boost::asio::io_context& io;
     sdbusplus::asio::object_server& objServer;