Upgrade server and Ansible

[justb4]

To enable working with Ansible we need:

• upgrade Ubuntu 18 to 20 (18 has Python2 and Python 3.6.9...)
• upgrade Ansible requirements and scripts
• add new Ansible script git.yml to remotely switch Git branch on server
• update Ansible README to reflect

In theory a new server could be bootstrapped in minutes with the Ansible bootstrap.yml (if one has SSH root access).

[justb4]

Done