Add network configuration rollback

[gibmat]

When configuring the network, a mistake can knock IncusOS off the network and there's currently no easy way to recover from this. We should add an option when setting the network configuration to automatically rollback after a configured period of time unless canceled. We'd then add some sort of "commit" or "confirm" API endpoint that would make the new configuration permanent.

Because of the complexity of network configurations, there's no way to automatically detect if a configuration is "good", either from the IncusOS side (ie, DNS checks, pings, etc) or from the client side (since the IP address(es) may change, etc). The user will need to run two different commands:

incus admin os system network edit

Then, after confirming that IncusOS appears correctly on the network:

incus admin os system network commit