refactor examples structure

CMakeLists.txt

 cmake_minimum_required( VERSION 3.24 )
 project ( sfg-walberla )
 
-option( SFG_WALBERLA_BUILD_EXAMPLES "Build sfg-walberla's examples" OFF )
-
 list (APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake )
 find_package( PystencilsSfg REQUIRED )
 
@@ -19,7 +17,3 @@ target_link_libraries(
     INTERFACE
     core stencil domain_decomposition blockforest field
 )
-
-if( ${SFG_WALBERLA_BUILD_EXAMPLES} )
-    add_subdirectory( examples )
-endif()
\ No newline at end of file

examples/CMakeLists.txt

+cmake_minimum_required( VERSION 3.24 )
+project( walberla-codegen-examples )
+
 include(FetchContent)
 
 FetchContent_Declare(
@@ -6,3 +9,8 @@ FetchContent_Declare(
 )
 
 FetchContent_MakeAvailable(walberla)
+
+add_subdirectory(${CMAKE_SOURCE_DIR}/.. ${CMAKE_BINARY_DIR}/sfg-walberla)
+
+add_subdirectory( PoiseuilleChannel )
+

examples/PoiseuilleChannel/PoiseuilleChannel.cpp

+int main(void) {
+    return 0;
+}