JSON exporter output cut short due to BufWriter size

[IncludeArthur]

Sometimes the output of the JSON exporter is cut short producing invalid JSON syntax that is difficult to parse.
If a timeout flag is specified, the exporter will eventually output all the data otherwise some data might be lost when Scaphandre is manually stopped. This happens both for stdout and file output.

I think that the problem is caused by the BufWriter default size of 8 KiB and the high amount of data produced by the JSON exporter.
I've also noticed that it takes a long time (up to 20 seconds on my hardware) between consecutive outputs leading to a lot of data accumulating in the buffer.

[bpetit]

Hi !

Thank you for documenting this issue, I tried a PR including a different initialization of the BufWriter, setting the size of the buffer.

Let me know if you can try this branch before it makes it to dev, I'd love to hear feedbacks.