[Design]: site-to-site VPN functionality

Currently, defguard supports only a "roadwarrior" setup (one server and clients connect to the server).
In the network tab, we need to be able to configure current setup (roadwarrior) and "site-to-site" VPN (where two servers communicate - no clients are connecting to this instance).
So we have "Add location" but now it would be setup VPN and we should choose which type.
After selecting site-to-site we need to have a configuration for two server endpoints this is a great visualisation that we should do in order to show the admin what should be configured:
```
┌─────── WireGuard site-to-site ──────┐
│ 10.10.9.0/31 │
│ │
10.10.9.0 wgA│ xx │wgB 10.10.9.1
┌─┴─┐ xxx xxxx ┌─┴─┐
alpha site │ │ext xx xx ext│ │ beta site
│ ├─── x x ───┤ │
10.10.10.0/24 │ │ xx xx │ │ 10.10.11.0/24
│ │ x x │ │
└─┬─┘ x x └─┬─┘
10.10.10.1│ xx x │10.10.11.1
...┌─────────┬────┘ xx xxx xx └───┬─────────┐...
│ │ xx xxxxx │ │
│ │ │ │
┌─┴─┐ ┌─┴─┐ public internet ┌─┴─┐ ┌─┴─┐
│ │ │ │ │ │ │ │
└───┘ └───┘ └───┘ └───┘
```