Feature - support multiple DB types

[bomoko]

This draft seeks to introduce supporting multiple database types out of the box.

It makes the following assumptions/attempts the following:

• The most basic/default setup is the current one, namely a mariadb-drupal lagoon image (such as uselagoon/mariadb-10.5-drupal)
• If one wishes to distinguish between a database, we use the DATABASE_TYPE environment variable, which is assumed to be either postgres, mysql, or mariadb
• Based on these types, we take our best guess at what the defaults for that DATABASE_TYPE is.