[FrameworkBundle] improve server:run feedback

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | 
| License       | MIT
| Doc PR        | 

In #12253, improved feedback was added to the `server:run` command
instructing the user how to terminate the built-in web server. This
is hereby backported to the `2.3` branch.