[DevKit] POS System API supports query of payment result via POST /PayResponse

[turtletramp]

With https://github.com/fiskaltrust/api-definitions/issues/39 new endpoint is documented on how to query payment result.

TODO:

• implement the request in the library ✅
• use it in the HOWTOs to query payment result so that it gets clear that this request can also be used after critical communication issues (like power outages on site or other) - ❓ work in progress but not testable at the moment; see below

[turtletramp]

2026-05-11:
BLOCKED: implemented into DEV Kit but I am not able to test it currently because of an issue in POS System API. See https://github.com/fiskaltrust/service-possystem-api/issues/124 for further details

2026-05-20: Paul informed me that the issue should be fixed but because of vacations and other issues the fix will be release during next week --> I expect that I can continue on this issue 1st June

[turtletramp]

Should be fixed in Sandbox now (based on Paul) --> lets check --> works now :)