py: add pyproject.toml to support PEP-517-compatible build-systems

py: add pyproject.toml to support PEP-517-compatible build-systems

commit 8e603e0f7eec7c0000344a004228a30fbf0ece5c upstream.

This makes it possible to build and install the module without directly
invoking setup.py which has been deprecated.

Retain the setup.py script for backwards-compatibility.

Update INSTALL to mention the new config-file.

Link: https://blog.ganssle.io/articles/2021/10/setup-py-deprecated.html
Signed-off-by: Jeremy Sowden <jeremy@azazel.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>