Add option to write log output to a timestamped log file.

We may want to preserve and/or share the outputs of running the various python scripts. Let's provide a consistent option to do so.

I'd suggest we auto-generate the filename and write it to the ./logs folder.
For now I hope we can rely and reuse the code we've got to detect the root of the repo to locate the {repo_root}./logs folder. This won't work as-is if we release this code e.g. as a pip package.
How about adding a --preserve-log command-line option to all the currently active scripts in ./src and ./utils?

commercetest / nlnet