ENH: chtMultiRegionFoam - add frozenFlow option

Adds frozenFlowOption into chtMultiRegion* solvers.

Meta-data

• EP1924
• Test case: multiRegionHeater.zip
• linux64ClangDPInt32Opt (clang11)
• linux64GccDPInt32Opt
• linux64GccSPDPInt64Debug
• Alltest: No new error/No change in existing output

applications/solvers/heatTransfer/chtMultiRegionFoam/chtMultiRegionSimpleFoam/fluid/readFluidMultiRegionSIMPLEControls.H

@@ -5,3 +5,5 @@
 
     const bool momentumPredictor =
         simple.getOrDefault("momentumPredictor", true);
+
+    simple.readIfPresent("frozenFlow", frozenFlowFluid[i]);