bpo-46285: Add command-line option -p/--protocol to module http.server

[geryogam]

This PR will add command-line option -p/--protocol to module http.server which specifies the HTTP version to which the server is conformant (HTTP/1.1 servers can now be run from the command-line interface of module http.server):

python -m http.server --protocol HTTP/1.1

https://bugs.python.org/issue46285

[merwok]

Thanks for the the PR! Let’s merge this one after the bug fix to the same module.

[merwok]

Please avoid rebases and force-pushes for CPython, github does not have a good experience for reviewers.
Regular merges are also easier to do!

[orsenthil]

LGTM.

I had a brief hesitancy for exposing this protocol version via flag as the support is not comprehensive. I am pretty sure we are missing many features.

But given that class supports .protocol_version as a attribute, exposing it via a command line flag is alright.

[geryogam]

Thanks @merwok, @JelleZijlstra, and @orsenthil for the review!