NethVoice: make it possible to copy a template model

Description

Add the possibility to duplicate an existing template model in NethVoice.

Currently, when a new template model is needed with settings similar to an existing one, it must be created manually from scratch.

A Copy/Duplicate action would make it possible to use an existing template model as a starting point.

Expected behavior

From the template model list, the user should be able to:

1. Select an existing template model.
2. Click a Copy or Duplicate action.
3. Create a new template model containing the same configuration as the original one.
4. Assign a new name to the copied model before saving it.

The original template model must remain unchanged.

Benefit

This would simplify the creation of similar template models and reduce configuration errors and duplicated manual work.