more dynamic definition of ‘built-in’ templates

### The required feature described as a wish

As a User/Admin/Operator I would like to install up to date builtin templates for new installations.

As a possible solutions it could not install any default or have it overwritten by a parameter or setting on installation or zone creation.

The issue names no files, tests, or entry points. Start by clarifying how built-in templates should be selected or overridden during installation and zone creation, then locate the relevant CloudStack workflows. Done should mean that new installations can use up-to-date templates and that the chosen default or override behavior is documented and tested.

Written by the indexing model from the issue text.