Provide semantic hint for browser to complete 2FA field

Browsers such as Safari can now generate one-time-codes for 2FA. Currently logging in to Docker Hub using Safari in this way is a little clunky.

If could be made much smoother by changing autocomplete="off" to autocomplete="one-time-code" in the appropriate input tag.

Reference: HTML attribute: autocomplete - HTML: HyperText Markup Language | MDN