fix: add CUSTOM_OBJFUNC to historyMap.py and CFlowOutput.cpp

- Add if (false) AddHistoryOutput for CUSTOM_OBJFUNC in CFlowOutput.cpp
  so the generator can pick it up in future
- Manually add CUSTOM_OBJFUNC entry to historyMap.py

Fixes #2586

Author: riddhi1228

SU2_CFD/src/output/CFlowOutput.cpp

@@ -1789,6 +1789,9 @@ void CFlowOutput::AddAerodynamicCoefficients(const CConfig* config) {
   AddHistoryOutput("AOA", "AoA", ScreenOutputFormat::FIXED, "AOA", "Angle of attack");
 
   AddHistoryOutput("COMBO", "ComboObj", ScreenOutputFormat::SCIENTIFIC, "COMBO", "Combined obj. function value.", HistoryFieldType::COEFFICIENT);
+  // CUSTOM_OBJFUNC is added here so historyMap.py knows how to get its
+  // value, the actual output is COMBO.
+  if (false) AddHistoryOutput("CUSTOM_OBJFUNC", "ComboObj", ScreenOutputFormat::SCIENTIFIC, "COMBO", "Custom obj. function value.", HistoryFieldType::COEFFICIENT);
 }
 
 void CFlowOutput::SetAerodynamicCoefficients(const CConfig* config, const CSolver* flow_solver){

SU2_PY/SU2/io/historyMap.py

@@ -310,6 +310,12 @@
         "HEADER": "ComboObj",
         "TYPE": "COEFFICIENT",
     },
+    "CUSTOM_OBJFUNC": {
+        "DESCRIPTION": "Custom obj. function value.",
+        "GROUP": "COMBO",
+        "HEADER": "ComboObj",
+        "TYPE": "COEFFICIENT",
+    },
     "DEFORM_ITER": {
         "DESCRIPTION": "Linear solver iterations for the mesh " "deformation",
         "GROUP": "DEFORM",