Improve Security of Remote Support Sessions

[gsanchietti]

Proposed changes:

1. Disable the remote support connection automatically after 24 hours.
   • Save the start of the remote session somewhere in the system (every place volatile is good enough)
   • Add a CLI command that allows the extension of such time, at the same time save that you extended the session
2. Show the session expiration time inside the UI.
   • The UI should be aware if the session has been extended
   • Needs changes/additional APIs
   • JSON for saving the first point? This could be easily then thrown to the UI.
3. Ensure SSH is reachable only from the support VPN.
   • Doubting this will work properly, let's give it a shot
4. Evaluate how to limit access to the web interface for the support user to only a specified list of IP addresses.
   • Probably not doable without killing access to unwanted users

[stephdl]

discussion at https://mattermost.nethesis.it/nethesis/pl/qt3xcy1i4bfnxrcmsnw5su59ta