Pulp

Consider the following scenario:

1. A user installs Pulp 3.1 with ansible-pulp.
2. When they specify pulp_install_plugins, they unknowingly specify 2 plugins: 1 that requires 3.1, and one that requires 3.0.
3. Pulp gets downgraded from 3.1 to 3.0, and does not function due to different ansible installer logic for the pulpcore version.
4. Even if they overcome the installer logic, the other plugin is now broken.

A similar problem can happen for the container builds.

I believe this should be mitigated by refusing to install a plugin that requires a newer version of pulpcore. It catches the problem early on before it becomes bigger. ("poka-yoke")

I propose a pip constraints file, generated to contain only pulpcore at whatever version of pulpcore installed, immediately after pulpcore is installed. All future pip install tasks will specify the constraints file.
https://pip.pypa.io/en/stable/user_guide/#constraints-files

For our ansible installer, we will use "extra_args" for the constraints argument.
https://docs.ansible.com/ansible/latest/modules/pip_module.html