[Components][HttpKernel] Add FINISH_REQUEST to events overview table

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes (symfony/symfony#8904)
| Applies to    | 2.4+
| Fixed tickets | #2959

It's not the whole doc for the event, but I've started by adding it to the events overview table, it needed a reformatting because of the long name.