Adding option to automatically installation

This extends FindPystencilsSfG.cmake with a Cache Variable CODEGEN_PRIVATE_VENV. This is set by default and if activate it creates a python venv and installs either dependencies from a requirements.txt or if this is not present it downloads the latest pystenicls-sfg/pystencils versions. If a custom Interpreter is passed to cmake this deactivated.

In external CMake Projects this files could by included via

## Pystencils-sfg setups
set(FIND_PYSTENCILSSFG_CMAKE_PATH "${CMAKE_BINARY_DIR}/_pystencilssfg-cmake/")
file(DOWNLOAD
    "https://i10git.cs.fau.de/ob28imeq/pystencils-sfg/-/raw/cmake_setup/src/pystencilssfg/cmake/FindPystencilsSfg.cmake?ref_type=heads"
    "${FIND_PYSTENCILSSFG_CMAKE_PATH}/FindPystencilsSfg.cmake"
)

SET ( CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} ${FIND_PYSTENCILSSFG_CMAKE_PATH})

find_package( PystencilsSfg REQUIRED )

standalone/CMakeLists.txt

@@ -54,20 +54,20 @@ if (CODEGEN_PRIVATE_VENV)
 			message( WARNING "Could not find ${CODEGEN_VENV_REQUIREMENTS}" )
 		endif()
 
-		# get the find pystencils-sfg file
-		execute_process( 
-			COMMAND ${PystencilsSfg_PYTHON_INTERPRETER} -m pystencilssfg cmake make-find-module
-			WORKING_DIRECTORY ${CMAKE_FIND_PACKAGE_REDIRECTS_DIR}
-		)
-		# renaming it
-		file(RENAME ${CMAKE_FIND_PACKAGE_REDIRECTS_DIR}/FindPystencilsSfg.cmake ${CMAKE_FIND_PACKAGE_REDIRECTS_DIR}/pystencilssfg-config.cmake)
-
-                # Find it
-                find_package( PystencilsSfg REQUIRED )
-
 		set( _sfg_private_venv_done TRUE CACHE BOOL "" )
 		mark_as_advanced(_sfg_private_venv_done)
 	endif()
 	set(_sfg_cache_python_init ${_venv_python_exe})
 	set(PystencilsSfg_PYTHON_INTERPRETER ${_sfg_cache_python_init} CACHE PATH "Path to the Python executable used to run pystencils-sfg")
 endif()
+
+# get the find pystencils-sfg file
+execute_process( 
+	COMMAND ${PystencilsSfg_PYTHON_INTERPRETER} -m pystencilssfg cmake make-find-module
+	WORKING_DIRECTORY ${CMAKE_FIND_PACKAGE_REDIRECTS_DIR}
+)
+# renaming it
+file(RENAME ${CMAKE_FIND_PACKAGE_REDIRECTS_DIR}/FindPystencilsSfg.cmake ${CMAKE_FIND_PACKAGE_REDIRECTS_DIR}/pystencilssfg-config.cmake)
+
+# Find it
+find_package( PystencilsSfg REQUIRED )