Add autocomplete to username and password login
### Feature Description

When logging into Homebridge on an Apple device, the password autofill isn’t triggered. It would be very convenient to have that work, and the effort is trivial: just add `autocomplete` to the HTML elements. See [the Apple doc](https://developer.apple.com/documentation/security/enabling-password-autofill-on-an-html-input-element) for details.