packer build fails when a template name is provided for the source_template option

Documentation for the source_template option in the cloudstack source block at https://developer.hashicorp.com/packer/plugins/builders/cloudstack says that "the **name** or ID of the template used as base template for the instance" is allowed. When using the name of the template, packer returns this error:

Error retrieving UUID of template : No match found for : &{Count:0 Templates:[]}

Only the ID of a template appears to be accepted. Need to be able to specify template name as well.

从 CloudStack 源块的 source_template 处理开始，并使用模板名称而不是 ID 来复现该失败。当模板名称按文档所述被接受，同时基于 ID 的配置继续正常工作时，此更改即完成。

由索引模型根据 Issue 内容生成。