Document external dependencies and their versions across the environments

[php-coder]

When we upgrade one of the external dependencies we shouldn't forget to update it on all environments. It would be helpful to have a list of such dependencies along with their versions across the environments.

Candidates:

• Ubuntu (CI, prod, docker-compose)
• JDK (CI, prod, docker-compose)
• MySQL (CI, prod, docker-compose)
• PostgreSQL (CI, prod, docker-compose)
• Python (CI, prod) (used by tools on CI and by Ansible)
• bash
• duplicity

Related issues: #1017, #1141, #1158, #1467, #1556