[Thread]Move the encoding of the thread diagnostics attributes to the app layer (#31766)

* Move the encoding of the thread diagnostics attributes to the app layer

* Restyled by whitespace

* Fix mtd build

* Fix some builds

* Fix general attributes read

* Apply suggestions from code review

Co-authored-by: mkardous-silabs <84793247+mkardous-silabs@users.noreply.github.com>

* address comment

---------

Co-authored-by: Restyled.io <commits@restyled.io>
Co-authored-by: mkardous-silabs <84793247+mkardous-silabs@users.noreply.github.com>

Author: 3 people

src/app/chip_data_model.gni

@@ -356,6 +356,12 @@ template("chip_data_model") {
           "${_app_root}/clusters/${cluster}/${cluster}.h",
           "${_app_root}/clusters/${cluster}/EnergyReportingTestEventTriggerHandler.h",
         ]
+      } else if (cluster == "thread-network-diagnostics-server") {
+        sources += [
+          "${_app_root}/clusters/${cluster}/${cluster}.cpp",
+          "${_app_root}/clusters/${cluster}/thread-network-diagnostics-provider.cpp",
+          "${_app_root}/clusters/${cluster}/thread-network-diagnostics-provider.h",
+        ]
       } else {
         sources += [ "${_app_root}/clusters/${cluster}/${cluster}.cpp" ]
       }