[Validator] Allow basic auth in url when using UrlValidator.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | 
| License       | MIT
| Doc PR        | 
Now an url with basic auth like ```http://username:password@symfony.com``` can be valid.
Should be `(([\pL\pN-]+:)?([\pL\pN-]+)@)?` then as the first part is optional and at least the second should exists with the `@` sign.