Use build-in modification of pip.conf

[TillBeemelmanns]

• Uses pip config command to edit /root/.config/pip/pip.conf
• https://pip.pypa.io/en/latest/cli/pip_config/
• No more collisions possible
• Previous behavior: Possibly two sections [global] in /root/.config/pip/pip.conf would have been created which causes pip to crash

Note that

# [Priority 1] Site level configuration files
#       1. `/usr/pip.conf`
#
# [Priority 2] User level configuration files
#       1. `/root/.config/pip/pip.conf`
#       2. `/root/.pip/pip.conf`
#
# [Priority 3] Global level configuration files
#       1. `/etc/pip.conf`
#       2. `/etc/xdg/pip/pip.conf`

Hence we need to execute:

# for /etc/pip.conf
RUN python -m pip config --global set global.break-system-packages true