Port forward: add GRE to supported protocols in the UI

[mamengoni]

Feature request
Add the GRE protocol to the list of supported options in the port forwarding section of the NethSecurity UI.

Why is it needed?
The GRE protocol is commonly used for certain types of network configurations.
Including GRE as a selectable option in the port forwarding UI would enhance the flexibility of the system and cater to additional use cases.

Proposed solution
Update the port forwarding UI to include GRE as a supported protocol, alongside TCP, UDP, and others.

Components
NethSecurity version: 8-23.05.5-ns.1.4.1