[TwigBundle] Add possibility to generate absolute assets urls

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT
| Doc PR        | https://github.com/symfony/symfony-docs/pull/3683

This is another approach of #7722

 - [x] Add unit tests
 - [x] Update doc
a ten plik po co? :D