EZP-20426 - Legacy cronjobs and scripts should be launchable from Symfony CLI

Ref https://jira.ez.no/browse/EZP-20426.
Related PR on legacy : https://github.com/ezsystems/ezpublish-legacy/pull/558

## Description
It's currently impossible to launch legacy cronjobs/scripts from Symfony context (`ezpublish/console`), which is a blocker is many cases (like HTTP cache clear operations during cronjobs execution).

One should be able to run a command like :
```bash
php ezpublish/console ezpublish:legacy:script bin/php/ezpgenerateautoloads.php
php ezpublish/console ezpublish:legacy:script runcronjobs.php frequent
```

## Tasks
* [x] Adapt `CLIHandler` to be able to use `run()` method
* [x] Create a console command to run legacy scripts
* [x] Make it possible to display help from legacy scripts
* [x] Ensure to be able to run legacy cronjobs correctly

## Known limitations
* If the script contains a *shebang*, it will be displayed as is
* Not possible to pass options considered as *standard* by Symfony Console to the legacy script (e.g. `--help`, `-e`, `-s`). Hence it's better to use expanded option names:

```bash
php ezpublish:legacy:script bin/php/ezpgenerateautoloads.php --extension --progress
```