Potential SS4 db config

db-config.yml

---
Name: msyql-database
Only:
  Env:
    SS_DB=mysql
---
SilverStripe\Core\Injector\Injector:
  SilverStripe\ORM\Connect\Database:
    class: 'SilverStripe\ORM\Connect\MySQLDatabase'
    properties:
      connector: %$PDOConnector
      schemaManager: %$MySQLSchemaManager
      queryBuilder: %$MySQLQueryBuilder
    calls:
      -
        - "connect"
        -
          - server: `SS_DATABASE_SERVER`
            username: `SS_DATABASE_USERNAME`
            password: `SS_DATABASE_PASSWORD`
            database: SS_ss4
---
Name: pgsql-database
Only:
  Env:
    SS_DB=pgsql
---
SilverStripe\Core\Injector\Injector:
  SilverStripe\ORM\Connect\Database:
    class: 'SilverStripe\Postgres\...'
---
Name: sqlite-database
Only:
  Env:
    SS_DB=sqlite
---
SilverStripe\Core\Injector\Injector:
  SilverStripe\ORM\Connect\Database:
    class: 'SilverStripe\Sqlite\...'

Lines 14-21 are pretty horrible but basically that stops you from needing to change the current connect() method