VPN-4987 [Part 1] - Check for internet connectivity upon activation + VPN-5994 - Inspector command

[Gela]

Description

This PR does 2 things:

1. Check for internet connection upon activation. This is the backend code only, frontend will be completed in a later sprint
2. Add inspector command force_connection_down to mock network connection being down.

Please note that functional tests cannot be added until the front end work is done.

Reference

https://mozilla-hub.atlassian.net/browse/VPN-5994
https://mozilla-hub.atlassian.net/browse/VPN-4987

Checklist

• My code follows the style guidelines for this project
• I have not added any packages that contain high risk or unknown licenses (GPL, LGPL, MPL, etc. consult with DevOps if in question)
• I have performed a self review of my own code
• I have commented my code PARTICULARLY in hard to understand areas
• I have added thorough tests where needed

[vinocher]

Looks good!