entity-manager: function for building inventory/system path

Tested: on QEMU/yosemite4 with adapted config.

```
root@yosemite4:~# journalctl | grep entity-manager
Apr 03 13:35:06 yosemite4 entity-manager[503]: Clearing previous configuration
Apr 03 13:35:07 yosemite4 entity-manager[503]: dbus command syntax error {"BOARD_MANUFACTURER": "(Quanta|Ingrasys)", BOARD_PRODUCT_NAME": "Ventura FAN Board", "BOARD_INFO_AM4": "adc-max"}
Apr 03 13:35:08 yosemite4 entity-manager[503]: dbus command syntax error {"BOARD_MANUFACTURER": "(Quanta|Ingrasys)", BOARD_PRODUCT_NAME": "Ventura FAN Board", "BOARD_INFO_AM4": "adc-max"}
Apr 03 13:35:08 yosemite4 entity-manager[503]: Inventory Added: Yosemite 4 Management Board
Aug 19 00:22:52 yosemite4 entity-manager[503]: dbus command syntax error {"BOARD_MANUFACTURER": "(Quanta|Ingrasys)", BOARD_PRODUCT_NAME": "Ventura FAN Board", "BOARD_INFO_AM4": "adc-max"}
Aug 19 00:22:59 yosemite4 entity-manager[503]: dbus command syntax error {"BOARD_MANUFACTURER": "(Quanta|Ingrasys)", BOARD_PRODUCT_NAME": "Ventura FAN Board", "BOARD_INFO_AM4": "adc-max"}
root@yosemite4:~# busctl tree xyz.openbmc_project.EntityManager
`- /xyz
  `- /xyz/openbmc_project
    |- /xyz/openbmc_project/EntityManager
    `- /xyz/openbmc_project/inventory
      `- /xyz/openbmc_project/inventory/system
        `- /xyz/openbmc_project/inventory/system/board
          `- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/All_Fan
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P0V6_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P12V_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P1V0_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P1V2_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P1V8_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P2V5_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P3V3_RGM_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P3V3_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P3V_BAT_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P5V_USB_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P5V_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_TEMP_C
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/PID_NIC_TEMP
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/Stepwise_MGNT_TEMP
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/Stepwise_NIC_TEMP
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/Stepwise_SENTINEL_DOME_SLOT_PRESENT_PERCENTAGE
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/Stepwise_VIRTUAL_NIC_TEMP_C
            `- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/Zone_1
```

Change-Id: I603ea4707e3a9078968b0f76e4a649feb9fdd1c0
Signed-off-by: Christopher Meis <christopher.meis@9elements.com>
diff --git a/src/entity_manager/utils.hpp b/src/entity_manager/utils.hpp
index 3bf20f2..b638239 100644
--- a/src/entity_manager/utils.hpp
+++ b/src/entity_manager/utils.hpp
@@ -34,4 +34,7 @@
     nlohmann::json::iterator& keyPair, const DBusInterface& interface,
     size_t index, const std::optional<std::string>& replaceStr = std::nullopt);
 
+std::string buildInventorySystemPath(std::string& boardName,
+                                     const std::string& boardType);
+
 } // namespace em_utils