python3: Split pip into separate source package

python3: Split pip into separate source package

Packaging pip from a separate source package allows it to stay updated
with upstream.

Host pip will remain installed as part of python3. Host pip is used in a
much more controlled way and so is less critical for it to track
upstream.

This also removes the python-pip-conf package and installs the pip.conf
file as part of python3-pip.

The patch 003-disable-pip-version-check.patch is originally from Debian:
https://salsa.debian.org/python-team/packages/python-pip/-/blob/bb079efb8c6dd2c284eee94cf90e61bce19a6f73/debian/patches/disable-pip-version-check.patch

pip was in a separate source package that was removed in
a53d0c5a403d1669e2cf6c59c2be6a9d3ed633a0; this work is not based on that
earlier package.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>