Proxito: test serving language like paths

[stsewd]

This will work once we remove this

readthedocs.org/readthedocs/proxito/urls.py

Lines 163 to 171 in eadf6ac

	re_path(
	(
	r'^(?:projects/(?P<subproject_slug>{project_slug})/)?'
	r'(?P<lang_slug>{lang_slug})/'
	r'(?P<version_slug>{version_slug})$'.format(**pattern_opts)
	),
	fast_404,
	name='docs_detail_directory_indexing',
	),

and make the new implementation the default.

Closes #8399

[humitos]

It seems we are pretty close to make this work, right?

[stsewd]

@humitos we are basically blocked on https://github.com/readthedocs/meta/issues/124

[stsewd]

I'm including this in #10660.