Allow several DB_ entries in .env

Summary:
Currently, .env files can received DB_ variables from a pillar section 'db'.
This change allows to define several of those sections.

Use case:
For Obsidian Workspaces, we also need to connect to Orbeon.

Ref T2160

Test Plan: Should be no-op

Maniphest Tasks: T2160

Differential Revision: https://devcentral.nasqueron.org/D3816