HMI processes RPC as unsuccessful in case of custom UNSUPPORTED_RESOURCE result code

[GetmanetsIrina]

Description:
HMI processes RPC as unsuccessful in case of custom UNSUPPORTED_RESOURCE result code

Precondition:
1. SDL and HMI are started
2. Mobile device connected
3. Mobile app is registered and activated
4. Go to Main HMI setting-> RPC Control ->registered app name
5. Set UNSUPPORTED_RESOURCE result code for some RCP(e.g. AddSubMenu, AddCommand)

Steps to reproduce:

1. Mobile app requests RPC (AddSubMenu, AddCommand) that has custom UNSUPPORTED_RESOURCE result code on HMI
2. SDL sends the request to HMI

Expected result:
HMI adds requested item and responds with UNSUPPORTED_RESOURCE result code in the error structure (maybe it should be result structure, but according to current logic HMI sends UNSUPPORTED_RESOURCE result code only in error structure)

Actual result:
HMI process RPC as an unsuccessful one and does not add requested item (AddSubMenu, AddCommand) to the app menu and responds with UNSUPPORTED_RESOURCE result code in the error structure, but SDL trit such result code as successful and responds to the mobile app with success=true according to the current SDL logic.
As a result, the mobile app has information that the requested item is successfully added, but in fact, HMI has no such added item.

Environment:
SDL: https://github.com/smartdevicelink/sdl_core/tree/develop (eaec9b4)
HMI: https://github.com/smartdevicelink/sdl_hmi/tree/develop (c50b0a7)
SPT: SyncProxyTester (20210407)

[Ypostolov]

@jordynmackool PR with fix is ready for Livio review. Thank you.