Add timestamps to output.txt

[anrossi]

It would be helpful to include on each line in output.txt, the timestamp of when the line was logged.

[marten-seemann]

Agreed. This sounds like a good idea.

This is how we capture the output:

quic-interop-runner/interop.py

Lines 138 to 140 in 43402af

	output = subprocess.run(
	cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT
	)

I assume one could somehow modify / wrap the subprocess.PIPE to have a timestamp added to every line.