Optional templateid param fails for KVM VM import

### problem

When importing a KVM VM via API and if a template is not specified, import fails with error,
**Template is needed and unable to use default template for hypervisor KVM**
Even though templateid parameter is specified as optional in the API documentation:
https://cloudstack.apache.org/api/apidocs-4.22/apis/importUnmanagedInstance.html

In UI, template is a required field though.

Documentation doesn't talk about this restriction on KVM
https://docs.cloudstack.apache.org/en/4.22.0.0/adminguide/virtual_machines/importing_unmanaging_vms.html

This is more of a documentation issue if the following block can not be updated:
https://github.com/apache/cloudstack/blob/4.22.0.0/server/src/main/java/org/apache/cloudstack/vm/UnmanagedVMsManagerImpl.java#L1605-L1607

### versions

4.22; Maybe other versions as well
Import VM

### The steps to reproduce the bug

_No response_

### What to do about it?

Either update the documentation or remove the restriction to use default dummy template.

先查看已記錄的 importUnmanagedInstance API 和 docs/en/4.22.0.0/adminguide/virtual_machines/importing_unmanaging_vms.html，接著檢查 UnmanagedVMsManagerImpl.java 中 1605-1607 行附近的內容，以確認 KVM 限制。與維護者確認預期結果是僅修改文件還是修改程式碼；當 API 文件和管理員文件準確描述 templateid 的行為時，即表示完成。

由索引模型根據 Issue 內容生成。