Proxito: allow custom path prefixes (#10156)
The implementation was changed to a more limited feature, path prefixes, they are simpler, and can be exposed to users, since they are plain strings.
Changes:
- Renamed some variables to match our new standard names
- The old implementation of this (urlconf) works together with the new implementation (current projects will continue to work).
- The resolver and unresolver have been adapted to support the new path prefixes
- `get_url_prefix` is meant to just get the prefix of the subproject, so it has been renamed to do just that.
Tests are passing on .com :)
There is also the question about what to do with the other views (the ones under`/_/`).
Opened https://github.com/readthedocs/readthedocs.org/issues/10181 to talk about that, that feature can be implemented in another PR.
And support for hiding the `language` component can also be implemented later https://github.com/readthedocs/readthedocs.org/issues/10307
Closes #7136
