bpo-39121: write gzip header OS information

[wungad]

https://bugs.python.org/issue39121

[the-knights-who-say-ni]

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[wungad]

All changes implemented.

[corona10]

@wungad

Sorry for the delayed feedback.
Can you rebase your PR?
I will merge it after conflicting is resolved.

[bedevere-bot]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

[serhiy-storchaka]

Sorry, but I do not think we need this feature. There is no any use case. This PR just makes the code more complex without necessity.