Saving credentials

### Problem

Capnet doesn't save credentials for a captive portal. For example, on a library, cafe or university wifi, I need to reenter my credentials every time I visit. Capnet should auto-connect to these networks.

### Proposal

Capnet should save the credentials for the network and log in automatically the next time it detects said network. If it isn't possible, it should at least autofill the credentials to make the experience more seamless for the user (remove a friction point).

From a privacy point of view, Capnet could ask the user, on the first login, if the credentials should be saved or not.

### Prior Art (Optional)

_No response_