Disconnect active VPN sessions on location change

[wojcik91]

Description

Disconnect active sessions whenever relevant config options are changed in location config.
For example when disabling/enabling MFA.
Also consider other relevant cases:

• network address change

[kchudy]

• Invalidate sessions after any attribute of the location (besides name) changed
• Display a warning for the admin that the sessions will be removed @Va1ter provide design for the warning in the Location form

[wojcik91]

For now I'll just add the warning modal.

We'll maybe consider actively disconnecting sessions again once we start working on #1725

[Va1ter]

@kchudy Need more context - what kind of message should be inside this warning, is this a critical action or now, etc