Add Ansible playbook for Toolforge deployment

This Ansible playbooks takes care of:

• Ensuring various directories exist, which follow the default layout [1]
• Checking out the latest code from Git repository
• Setting up crontabs (in the no-so-right places)

It unfortunately does not install/update the Python requirements,
as this needs to be done in a Kubernetes shell, which apparently
only works in interactive mode.

[1] https://wikitech.wikimedia.org/wiki/Help:Toolforge/Web#Python_(uWSGI)