Development environment

• devenv configuration to create a LXC container
• Install npm global with yarn (needed by the backend) and pnpm (needed by Etherpad)
• Install PostgreSQL, create the users and the DBs needed by the backend and Etherpad
• Install Etherpad
• Update the README

playbooks/deploy.yml

+---
+- name: Deploy
+  hosts: acoords
+  become: true
+  become_user: "{{ app_user }}"
+  roles:
+    - role: deploy