[website] Broken links to some download packages

[Jennifer88huang-zz]

Describe the bug
When I check the Pulsar website with link check tool, I've found some broken links to download packages. I've fixed the ones i could. Could someone give some help on the ones with red boxes? The following is part of the report from https://www.drlinkcheck.com/

[Jennifer88huang-zz]

@tuteng could you give some help? Thank you.

[tuteng]

I think this css file https://github.com/cckellogg/incubator-pulsar/blob/26d7dfbc651353f91eea4ecf0400685c331eaf5c/site2/website/static/css/code-blocks-buttons.css can be added, but some download links I tested are normal.
https://archive.apache.org/dist/incubator/pulsar/pulsar-1.20.0-incubating/apache-pulsar-1.20.0-incubating-src.tar.gz
https://archive.apache.org/dist/incubator/pulsar/pulsar-1.19.0-incubating/apache-pulsar-1.19.0-incubating-src.tar.gz

But some file names are wrong, I think you can try to fix it.

[Jennifer88huang-zz]

Yes, when you click https://archive.apache.org/dist/incubator/pulsar/pulsar-1.19.0-incubating/apache-pulsar-1.19.0-incubating-src.tar.gz, it works; however, when you click sha512 under that package, it does not work. The asc links work well.