flask has migrated to using pyproject.toml, so we need
python_setuptools_build_meta instead of setuptools3.
Changelog: https://flask.palletsprojects.com/en/2.3.x/changes/#version-2-3-0
Signed-off-by: Trevor Gamblin <tgamblin@baylibre.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>
