[feat] Add trailing slash to package directory links at root index

[rpatterson]

This is useful, for example, with nginx proxy configurations, such as using the
ngx_aws_auth module, where directory paths can't be detected by the server.

[naiquevin]

Hi, @rpatterson. Can you please share your nginx config? Not sure I understand the problem correctly. We are also using the ngx_aws_auth and haven't faced any issue with trailing slashes. We have a blog post explaining our approach here - https://medium.com/helpshift-engineering/private-python-package-index-with-zero-hassle-6164e3831208

[rpatterson]

I've moved onto another approach, so the nginx config isn't easy for me to get ATM. I might be able to dig it up, but let me clarify from memory and see if that is enough for you.

The issue that this fixed is if I visited the root /simple/ PyPI index URL that lists all the packages in the index. The packages there should link to the package-specific URL that lists the available versions and dists. The root /simple/index.html generated by this package linked each package to a URL without a trailing slash, /simple/foo-package. But since nginx is proxying to S3 and has no insight into the type of resource available at a given path without a trailing slash, it would just proxy that request onto S3 which would accurately reply that the path wasn't a key for an S3 object.

This isn't an issue for pip since it goes straight to /simple/foo-package/ but I just thought the links in the generated /simple/index.html should work as well should anyone ever browser their own private PyPI in the browser.