✨ feat(Makefile): add build_and_install target to build and install package without running it

The path to the langflow.main module was incorrect, causing the backend target to fail. The path has been updated to the correct location.

The build_and_install target has been added to build the package and install it without running it. This is useful when the package needs to be built and installed on a remote server.
🐛 fix(Makefile): fix path to langflow.main module in backend target