Add support for socks connection to Git backend

[arthanson]

Fixes: #17639

Note: will also need to install the python_socks library along with the Dulwich library to use this:

pip install dulwich
pip install python_socks

To test locally, start a socks proxy in a docker container. Make a HTTP request and observe it using the proxy:

$ docker run -d --name socks5 -p 1080:1080 serjs/go-socks5-proxy
$ docker logs -f socks5

Specify the local proxy in Netbox configuration.py:

HTTP_PROXIES = {
   'http': 'socks5h://localhost:1080',
   'https': 'socks5h://localhost:1080',
}

Add a remote GIT datasource and you should see the traffic logs in the terminal. Setup a DataSource in Netbox, I was using the following in the form:

Name = GitSync
Type = Git
URL = https://github.com/bogdancordos/netbox_scripts.git

The URL just has a selection of scripts so you can see that it actually syncs the data source. Press the [Sync] button and make sure it actually syncs.

For SOCKs auth scenario it can be setup as follows:

docker run -d --name socks5 -p 1080:1080 -e PROXY_USER=aaa -e PROXY_PASSWORD=bbb  serjs/go-socks5-proxy

Then in configuration.py:

HTTP_PROXIES = {
    'http': 'socks5h://aaa:bbb@localhost:1080',
    'https': 'socks5h://aaa:bbb@localhost:1080',
}

[jeremystretch]

I've tested this both with and without authentication, and syncing worked as expected both times. Nice work @arthanson!