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.

先查看已记录的 importUnmanagedInstance API 和 docs/en/4.22.0.0/adminguide/virtual_machines/importing_unmanaging_vms.html，然后检查 UnmanagedVMsManagerImpl.java 中 1605-1607 行附近的内容，以确认 KVM 限制。与维护者确认预期结果是仅修改文档还是修改代码；当 API 文档和管理员文档准确描述 templateid 的行为时，即表示完成。

由索引模型根据 Issue 内容生成。