Install Pulp CLI in CI container

When we upload packages to pulp, we'll do it using their cli. This installs the cli and required config file. For now, the only thing we change in the config file from a default configuration is the base_url, to point to our pulp instance.

Note that eve though I install the config here, over here I provide a command to create a config file which will clobber this config file. Thew command approach is more flexible in that it make it possible to change the base_url, user, and password without having to make a new release of the base image.

Closes https://gitlab.com/gitlab-org/ci-cd/runner-tools/base-images/-/work_items/7+