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.

该 issue 没有指出文件、测试或入口点。首先明确在安装和创建区域期间应如何选择或覆盖内置模板，然后定位相关的 CloudStack 工作流。完成的标准是：新安装可以使用最新模板，并且选定的默认或覆盖行为已被记录并经过测试。

由索引模型根据 Issue 内容生成。