Support python3 language identifier (Pygments lexer name) in literalinclude/code-block

[cmarqu]

(Thanks for this awesome extension, I was always looking for something like this, and now I found it ;))

Issue

python3 as a language identifier/Pygments lexer name doesn't seem to be supported.

Expected behavior

Both python3 and python should work the same.

Actually, according to https://pygments.org/docs/lexers/#pygments.lexers.python.PythonLexer, there are more names (python, py, sage, python3, py3, bazel, starlark, pyi), maybe they should all be supported (especially py3)?

Steps to reproduce

I am using .. literalinclude:: python3 or .. code-block:: python3, and I don't see sphinx-codeautolink taking effect.
However, if I change these lines to .. literalinclude:: python and .. code-block:: python respectively, it's working as expected.

[felix-hilden]

Hi! Thanks for submitting the issue. If they are really just synonyms for the same lexer then there's no reason for us not supporting them! Contributions are welcome if you're up for it, but if not I should get to it within a couple of weeks 👍