[AVM Module Issue]: Clarification on `vmTemplate` parameter usage and session host deployment for Host Pool module

### Check for previous/existing GitHub issues

- [x] I have checked for previous/existing GitHub issues

### Issue Type?

Bug

### Module Name

avm/res/desktop-virtualization/host-pool

### (Optional) Module Version

_No response_

### Description

While working with the [avm/res/desktop-virtualization/host-pool](https://github.com/Azure/bicep-registry-modules/tree/main/avm/res/desktop-virtualization/host-pool) module, I noticed that the `vmTemplate` parameter is included in the inputs, but there’s currently no documentation on how to use it. Additionally, when I pass a value to it during deployment, it doesn’t seem to have any effect - no session hosts are created or triggered.

I have a few questions:
- Could you please clarify the intended usage of the `vmTemplate` parameter?
- Is there any planned support for provisioning session hosts automatically via this module?
- What is the recommended or suggested practice for adding session hosts when using this host pool module? Should it be handled in an additional step (e.g. with the virtual machine module)?

It would be great to either document, mark or remove the parameter if it’s currently not functional, to avoid confusion.

Thanks in advance!

### (Optional) Correlation Id

_No response_

Start with the avm/res/desktop-virtualization/host-pool module entry point and inspect how the vmTemplate input is currently handled during deployment. Confirm whether it affects session-host provisioning, then document its intended usage or clarify that session hosts require an additional step; done means the parameter's behavior and recommended deployment practice are unambiguous.

Written by the indexing model from the issue text.