Allow changing URL password

[bittrance]

When a GitHub app wants to clone a private repo, it is required to pass the access token as a part of the URL https://docs.github.com/en/apps/creating-github-apps/authenticating-with-a-github-app/authenticating-as-a-github-app-installation 😒 . A gix-url user may want to use Url to store the validared Url internally, but the access token is retrieved at runtime, so such an application will want to clone the Url and set the password just before fetching the private repo.

[Byron]

Thanks a lot! Now the API is finally symmetric.

gix-url started out a little bit restrictive about password to the point where one couldn't even query them, but fortunately these dark ages are over now :).