NethVoice: Add Proxy URL and Port to the summary window for custom devices

[mgarra]

Description:
Currently, in the Device Configuration → Custom Device Assignment section of NethVoice, there is a summary window displaying the necessary information to manually configure non-provisioned phones.

This window already includes useful data for setting up the devices, but it lacks an important element: the Proxy URL and the corresponding Port.

Request:
Add the following information to the summary window for custom devices:

• Proxy URL (e.g. sip.example.com)

• Proxy Port (e.g. 5061 or the actual port being used)

Reasoning:
These values are essential for manually configuring non-provisioned devices, as they allow users to correctly complete the SIP settings on their phones.

[tonyco97]

Testing version: https://github.com/nethesis/ns8-nethvoice/releases/tag/1.5.4-testing.23