distrobox-export has no host-to-container direction

**Edit:** `distrobox-host-exec(1)` does document a way to do this - *"you can symlink a command name to distrobox-host-exec and then call that command by its name"* - which I missed when filing. So the mechanism exists; what is missing is the management around it. Narrowing the request accordingly.

`distrobox-export` moves things one way only: out of a container and onto the host (`--app`, `--bin`, with `--list-apps`, `--list-binaries` and `--delete` to manage them). For the other direction there is the symlink trick, and nothing else.

The difference in ergonomics between the two directions is the point:

| | container -> host | host -> container |
|---|---|---|
| create | `distrobox-export --bin /usr/bin/foo` | symlink it yourself, in the right directory |
| list | `--list-binaries` | nothing |
| remove | `--delete` | `rm`, if you remember where you put it |
| marked as managed | `# distrobox_binary` in the wrapper | nothing |
| where it goes | `~/.local/bin`, or `--export-path` | your problem |

That last row is not a small thing: the symlink has to be somewhere the **container** has on `PATH` and the **host** does not. The shared home fails that test, and the failure is a message saying the command was not run inside a container when it was (filed as #2207). `/usr/local/bin` inside the container works, but needs root there and is lost when the container is recreated.

### What I would like

Something in the shape of the existing export, run inside the container:

```
distrobox-export --host-bin docker
distrobox-export --host-bin docker --delete
distrobox-export --list-host-bins
```

writing the symlink or wrapper into a container-only path, marked with a comment the way `--bin` marks its wrappers, so it can be listed and removed like anything else distrobox put there.

### Why it comes up

A container built for one job often needs a tool that belongs to the host and that the container should not own - in my case a development container driving the host's `docker`, with everything else about it isolated.

For docker specifically there is a neater answer that needs no bridge at all: with rootless docker, `/run/user/$UID/docker.sock` is already visible inside the container and owned by the same user, so pointing `DOCKER_HOST` at it is enough. That does not generalise to other host tools, which is why the export direction still seems worth having.

Version: distrobox 1.8.2.5, podman 5.8.4, Fedora 44.

Esamina lo script distrobox-export per capire come attualmente esporta binari e app dal container all’host. La nuova funzionalità comporterebbe l’aggiunta di flag come --host-bin, --list-host-bins e --delete per le esportazioni dall’host al container. Verifica come vengono creati i symlink tramite distrobox-host-exec e dove dovrebbero essere posizionati (in un PATH riservato al container). Inizia esaminando la logica di esportazione e poi progetta i nuovi comandi per gestire i symlink in modo simile, assicurandoti che siano contrassegnati come gestiti e possano essere elencati/rimossi.

Scritto dal modello di indicizzazione a partire dal testo della issue.