NethVoice Proxy: add GNR trunks configuration interface

[Amygos]

Configuring trunks without registration (commonly referred to as GNR) is
essential for creating routes based on the dialed numbers.

Requirements

A user interface is required to specify the trunk numbers and define which
NethVoice system should handle the forwarded calls.

The configuration must support specifying numbers using a prefix, enabling
multiple numbers to be managed with a single setting—an approach typical for
GNR setups.

A trunk configuration consists of the following elements:

1. A prefix for the trunk
2. A NethVoice module instance to which the trunk should be forwarded

User Interface Requirements

The UI should allow for the following:

1. Listing all configured trunks
2. Adding a new trunk
3. Editing an existing trunk
4. Deleting a trunk