Non-interweaved output for simple logger

Hi,

simple-logger currently interweaves output as it comes in, but it would be cleaner if the stdout/stderr was output after the execution is done.

I found a TODO in the code for simple-logger
https://github.com/google/wireit/blob/main/src/logging/simple-logger.ts#L238

I don't know the repository very well but I figure this should be quite easy to implement, just add a map with the label as key and an array of { stream: 'stderr' | 'stdout'; data: string | Buffer } as it's value and then on success/failure output the contents of the array, if present.

As for services I guess their logs should be output as they come in still though.