[Components][DependencyInjection] add note about a use case that requires to compile the container

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets |

As @movetodevnull pointed out in symfony/symfony#10045, the compilation chapter of the DependencyInjection component doesn't give any concrete use case of when it is absolutely needed to compile the container.

We should decide whether or not it makes sense to extend this note, once #3753 is getting merged.