Add a neutral networkingMode in C:\Users\user\.wslconfig

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**Is your feature request related to a problem? Please describe.**
Cannot tell WSL2 to leave eth0 alone, that is don't set IP address, mask, routes.

**Describe the solution you'd like**
Some setting in .wslconfig like: `networkingMode = noip`

**Describe alternatives you've considered**
Add this to /etc/wsl.conf
```
[boot]
command = ip address flush dev eth0
```

**Why?**
Because being unable to make `networkingMode = bridged` work, I resorted to this solution:

1. wsl --shutdown
2. open Hyper-V Manager / Virtual Switch Manager
3. click on Virtual Switches / WSL
4. enable External Network and select the LAN interface
5. Click Apply
6. Start WSL Ubuntu 22.04.2
7. `sudo -i`
8. `vi /usr/lib/systemd/network/wsl_external.network`
```
[Match]
Name=eth0
[Network]
Description=WSLBridge
DHCP=true
```
9. `vi /etc/wsl.conf`
```
[boot]
systemd=true
```
10. `echo "nameserver 192.168.0.1" > /etc/resolv.conf`
11. `systemctl enable systemd-networkd`
12. `systemctl enable systemd-resolved`
13. `wsl --shutdown`
14. Start WSL Ubuntu 22.04.2
15. `ip addr` shows that eth0 has **two** ip addresses: 172.x.x.x.x and 192.168.0.x (the first I believe is related to NAT)
16. `ip route` shows **two** default routes

**Additional context**
WSL version: 2.1.5.0
Kernel version: 5.15.146.1-2
WSLg version: 1.0.60
MSRDC version: 1.2.5105
Direct3D version: 1.611.1-81528511
DXCore version: 10.0.25131.1002-220531-1700.rs-onecore-base2-hyp
Windows version: 10.0.19045.4412

Start by reviewing the requested .wslconfig networkingMode setting alongside the /etc/wsl.conf and /usr/lib/systemd/network/wsl_external.network examples in the issue. Determine how a neutral mode should leave eth0 without an address, mask, routes, or duplicate default routes; done means the configuration is documented and the resulting interface state matches that behavior.

Written by the indexing model from the issue text.