fix: set alternatives to python3 for RHEL8

[PACordonnier]

Which issue(s) this PR fixes

Fixes #75

Additional comments

This change raises an issue when running ansible up to 2.12.

[DEPRECATION WARNING]: Distribution centos 8.7 on host edge-01 should use /usr/libexec/platform-python, but is using /usr/bin/python for backward compatibility with prior Ansible releases. A future Ansible release will default to using the discovered platform python for this host. See 
https://docs.ansible.com/ansible/2.9/reference_appendices/interpreter_discovery.html for more information. This feature will be removed in version 2.12. Deprecation warnings can be disabled by setting deprecation_warnings=False in ansible.cfg.

I think we should specify somewhere to use ansible_python_interpreter=auto . I think its location is in the ansible.cfg in getting-started

Agreements

• [x] I hereby declare this contribution to be licensed under the Apache License Version 2.0, January 2004.
• [x] I hereby agree to grant TOSIT a copyright license to use my contributions.

[rpignolet]

As discuss, many pros, many cons, so merge and yolo