XFN Runner: Show STDOUT of failed composition function (exit code >= 1)

### What problem are you facing?

We've implemented a function similar to the example functions from [docs](https://docs.crossplane.io/master/concepts/composition-functions/#an-example-function). If this functions fails, it returns a exit code greater than 0 and prints the error message in STDOUT.

```
[..] "error": "cannot run Composition Function pipeline: cannot run function \"service-versioning\": cannot run container: rpc error: code = Unknown desc = exit status 1: xfn: error: spark.Command.Run(): OCI runtime error: exit status 1"
```

Currenty, I cannot debug a composition function that fails to execute. When the function in the OCI container fails, I see the exit code but no additional information printed in STDOUT.

### How could Crossplane help solve your problem?

Provide a way to see the STDOUT of functions that failed. That may be behind a flag/option like verbosity level/debug mode, etc.
Perhaps, also STDERR could be used, as it would be the more appropriate place for error messages.

No source file or test is named in the issue. Start by locating the OCI container execution path and reproduce a composition function that exits nonzero while writing to STDOUT; determine how failed output should be exposed, including whether STDERR is handled, and add coverage showing that the diagnostic text is visible.

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